Start with some root cause analysis, e.g.,

What is changing about your water supply at this time / temp?
Is balance fresh/recycle changing?
Where does fresh/recycle water come from?
What routine water analysis is being done? Have you attempted to characterize species in the water as temperature changes? Have seen in past where organics tended to decay / volatilize more in the hot/warm months & their presence in winter resulted in issues?
What changes are you making with frother additions to address the issue?

Understanding root cause is key to solution. 

Do you use wood in the mine to stabilize openings? Humic acid generated by decay of wood will create a very tenacious froth. If you have a wet/dry seasonal change, that may be the cause of the problem.

It sounds like you talking out of experience. Will humic acid be detected by simply checking the pH or alternatively how do I check for this? We didn't have a wet/dry seasonal change but this has happened the previous winter as well. Do you know how to combat the effect of the humic acid if it is the cause to the problem?

As of yet we have not found anything out of the ordinary on our water analysis (then again the water analysis is not really focused on organic material). Our recycled water basically comes from a tailings return dam and then we also receive water from another pond. Regarding the frother, currently we are not dosing frother at all.

I worked in Butte Montana where open pit workings intersected old underground workings. The ore produced froth that would pile up under the float cells as much as eight feet deep. The only thing that worked was a fresh water spray to dilute out the froth. Fine high velocity spray would beat down the froth in the launders to some extent; however an easy solution eluded us. Use of a froth breaking chemical (Aerodri) was discouraged as it caused a loss of recovery.

Serious effort to pick out wood from the ore before grinding would be of help as would prewashing the ore if water and infrastructure is available.

Have you looked into froth stability in relation to temperature? At one stage I was looking into utilizing the heat generated from our powerhouse and I came across a paper discussing froth stability and temperature and that you can break froth down by heating it up.

I don't remember the name or title of the paper sorry.

Some sites run into problems in winter due to the increase in concentration of reagents and other molecules in their raw and/or recycle water. What recommended above is what I would be investigating first as a fact finding mission.

We have ruled out the fact that it is only due to a drop in temperature, as the froth stability issue is still present when the slurry is immediately floated after exiting the mill.

We are definitely looking into the water cycle, as of yet we just haven't found anything that could cause this problem. 

Probably a solubility of some organic reagents (its "not slated" parts) drops drastically at below 10C. Thus you get a lot of hydrophobic micron and submicron particles armoring the bubbles surface.

I myself have not studied this aspect may be the following.

Theoretical: lowering the temperature of the pulp is accompanied by increased formation of foam, obtaining more stable foam, increasing the viscosity of the medium.

On one of the factories in the flotation of apatite by fatty acids also there is a problem (namely, when the temperature is below 10 ° C).

My idea: Make experiments with cold and hot water in one season time. Then we will know whether the theory of law. And be sure to tell us.

Is the problem arising in the primary rougher, secondary rougher or cleaning circuit or across the entire float circuit? UG2 plant or Merensky? What frother are you using? In fact, what are your reagent suite, frother, activator, collector and depressant? There can be any number of factors relating to the recycle water from tailings, internal recycle water, and buildup of reagents due to reduced dilution from summer rain or reduced sunlight. More detail required, if possible.

Does the problem go away with addition of rain/fresh runoff water? Does the circuit start to stabilize when the temperature starts to increase towards 20 degrees C?

To answer your question: no and no. We are frequently topping up our water circuit with fresh water (drinking water) as it is winter and we are not receiving rain, yet the problem still persists.

During the day when the temperature increases to around 20-25'C the problem is still present. What we experienced last year is that the problem only started going away round about September to October. However I suspect it is not due to rainfall as our rainfall season only starts December to January. The only thing I am sure of is whatever is responsible for the problem is definitely accumulating in the water circuit. 

My question was slightly ambiguous. My fault. Are you referring to the air temperature or the re-circulating water temperature? What percentage of fresh water compared to total volume are you replacing? Have you done any hardness tests on either the fresh or re-circulating water? Have you noticed an increase in consumption in your scale control program (if used)?

In the book "Fundamentals of the theory of flotation" there is the following information:

"The stability of the foam is affected by:

Concentration of the foaming reagent in the pulp;
Temperature of the pulp;
Size of the bubbles;
Concentration of the particles in the slurry;
Size of the particles;
Shape of the particles;
Degree of hydrophobicity of the particles.
Lowering the temperature usually increases the strength of the foam."

In addition, decreasing temperature also decreases the speed of the chemical reactions:
Reduces the solubility of the foaming reagent (frother) in a water;
Decreases the rate of decay (decomposition) of the foaming reagent.

This implies that the problem is accumulated in the reservoir. In this you are right. I think that in the cold period does not have time to decompose the foaming reagent. When you add a frother in the flotation again and again, you have the excess of concentration of the foaming reagent.

In practice, the excessive concentration of the foaming reagent results in very stable foam and the flotation performance deteriorates.

If this is true, need:
To reduce the concentration of the foaming reagent,
To dilute the solution with fresh water,
To replace the foaming reagent to frother weaker.

I presume that the process water uses a high proportion of water reclaimed from the tailings pond? The phenomenon you are describing is quite common with high proportions of reclaimed water consumed in the process.

Frothers are volatile compounds to varying degree. It is likely that the frother used in the process does not volatilize easily in the tailings pond when the temperature drops below 10oC. Also, surface tension (the fundamental principle in which frothers does what they do) is temperature dependent.

Anyways, if the over-frothing situation for temperatures less than 10oC can be overcome by reducing the frother addition made to the process, than it would be fairly easy to implement an appropriate control loop to account for this in the process control system.

Sorry we don't have experience at this temperature. But we did R&D in commercial COLUMN FLOTATION. Minute bubbles of 1mm were washed with shower of low pressure water on froth bed of 500 to 1000mm thick. We noticed that froth was SABLE. You too can try in your lab, or pilot plant.