A few things may help:
If you remove or keep the weedy species trimmed way back, the plants like Erio setaceum and Tonia will do much better. Red pantanal will branch and lose color with poor CO2. It will out compete most other plants in the tank if the CO2 goes bad. Generally, you want to make sure those plants do not get over shadowed by the other stem plants. Crypts, Anubias, Buce, Starougyne, they do not care much. Soil might help as I've said before, but cost is a factor.
CO2 degasses at a faster rate at higher temps, and.............plants GROW FASTER when the temp is higher. 20-50% faster by say a 10 C degree difference, so that's a lot more CO2 demand.
Say the tank is 21C in winter with stem plants like this, moderate light.
Summer it's 29C, if you had say 20 ppm of CO2 in the winter, things are okay.
Summer? You'd need to add at least 30 ppm to have the same effect, you'd also see higher rates of growth as well in summer vs winter.
Degassing increases non linearly as temp increase. This is true for all gases, so there is maybe 10-20% less O2 in the summer vs the winter with the same type of temp variation.
It is NOT that many plants do not LIKE warmer temps, it is that the hobbyists does not account for plant physiological changes that come with an increase in temps.
Valves have more thermal expansion in summer also, not much, but could be enough depending.