Conditional formatting seems to forget\reset their style after each sheet reopening. If you created and selected some styles, Calc automatically creates and selects various "ConditionalStyle_NN". It's a minor issue, but it messes with your Styles and make managing them pointless.
What file format do you use to save? Please attach a sample file, reduce the size as much as possible without private information, and paste the information in Menu/Help/About LibreOffice, there is a copy icon.
Created attachment 203681 [details] cond form style test.ods ods format works
Created attachment 203682 [details] cond form style test.xlsx xlsx doesn't work
I'm using .xlsx for compatibility. But I made the tests and noticed that .odt works, while .xlsx doesn't. I attached them
Version: 25.8.2.2 (X86_64) Build ID: d401f2107ccab8f924a8e2df40f573aab7605b6f CPU threads: 16; OS: Windows 10 X86_64 (build 19045); UI render: Skia/Raster; VCL: win Locale: it-IT (C); UI: en-US Calc: CL threaded
Created attachment 203692 [details] Screenshot with both files view I can't see any difference between both files.
Please test in safe mode, Menu/Help/Restart in Safe Mode
The difference is only visible if you open the Conditional Formatting panel and check the Style
Please review tdf#148489 *** This bug has been marked as a duplicate of bug 148489 ***