This has happened to me in multiple versions of PSPad, like 4.x, 5.0.0, on Windows 7, and Windows 10. But it has only happened on .pl (Perl) files (since that's what I edit the most with PSPad).
Highlighter used: Perl Completion of chars {[: not used (off) It might only happen once every 3-6 months, after 100s of hours of editing so it can be a tricky issue to track down. Other stuff: I will often leave PSPad running for weeks at a time without restarting it and without rebooting my PC. I do put my PC in sleep mode every evening. I wonder if this might be a variable to look at. -- <https://forum.pspad.com/read.php?2,75694,75889> PSPad freeware editor https://www.pspad.com