Hi Annie, when did you last lubricate the zips?
If its a while then it's worth getting an old stub of a candle ( or even a new candle if thats all you have handy) and rub carefully the teeth of the zip with the candle so its all well coated with candle wax (do both the inside of the zip and the outside..... ) then during the day zip and unzip the newly waxed zip half a dozen times so that the candle wax gets right into all the little crevices..... any excess wax can easily be wiped away with cloth.
There are special lubricants available for zips, but the candle wax stub is usually a "free" item that would other wise be thrown out, doesn't soil clothes or hands and is very effective at freeing up the zip for a smoother close or unclose either during the day or at night....
I suspect that the evening, zip troubles may be connected with contraction & expansion by tiny amounts, probably of both the zip and the material of the awning due to temperature and moisture changes. The changes in dimensions/tensions although tiny are often sufficient to cause the problems you describe. THe candle wax lube may be just sufficient to overcome the problem at zero cost... but do make sure that the whole length of the zip is treated...
Let us know if the candle stub "lubrication" does the trick for you.
Regards
paws
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