I think size is the key, I have 2 files with more than 1 and 2 MB on which this happens. It works fine with all other files and worked well with older versions with these as well.
It is no fatal bug, highlighting can be switched on immediately via "Change Syntax" dialog, but it annoys. -- <https://forum.pspad.com/read.php?4,74102,74102> PSPad freeware editor https://www.pspad.com
