I've been using these textures for so long! You are doing such fantastic work- don't let it stress you! If you have to attend to other things first then that's what you gotta do .
The customizer is so much fun! I've only run into a single issue- when I use a pack from the customizer, my single chests are a little messed up- the lid of the chest looks like its upside down. It only happens for single chests, normal, trapped, and ender, but not double chests. The specific chest textures I am using are from the Fantasy pack, and the browser I am using is Firefox. I am playing in 1.15.2. (Also, when I use a custom texture pack, my minecraft menu says its incompatible, but this is the only problem I've run into, so I'm not super worried about that.)
You are doing gods work. I wish you the best, thank you so much for what you're doing.
Edit: after some experimenting, it happens with any chest texture I use, if that helps at all.