Sash Windows sticking?

I had my windows painted about 2 months ago and unfortunately the downstairs window appeared to be painted shut which was quite upsetting as i had it professionally repaired to be functional again and im about to begin the gruelling task of unsticking it myself soon (if anyone has any tips for this pls let me know) however i went to open the bottom half of my windows upstairs and both windows are also stuck on the bottom half! I have had the bottom half of the windows open before but it genuinely looks like in certain spots the paint has stuck its self together when i know i have opened them before!
Is it the paint that was used?
Is this going to be an ongoing issue where my windows just stick shut if they aren’t permanently open?
Is this just a thing that happens with sash windows?
Was it the heat?
The paint used was BEDEC Multi Surface Paint in satin white
and my windows are the original wooden sash windows

I feel like im going crazy why are they sticking shut!!!