5.1.7 is the last version that actually applies forum styles.
I’m specifically referring to the styles set in the tabs for:
Forum Index Styling
Topic Index Styling
Topic/Reply Display
Maybe more, but those are the core ones.
I reverted back to 5.1.8 first. Styles not applied, Hitting the “save” button on those tabs has no effect.
Reverted back to 5.1.7. Styles not applied. Hitting the “save” button on those tabs works and reapplies styles to the frontend.
Tried to update to 5.1.8 again. Styles not applied, hitting the “save” button on those tabs has no effect.
Tried to update to 5.1.9 again. Styles not applied, hitting the “save” button on those tabs has no effect.
Only 5.1.7 is the last version applying styles for me, and I have to hit the “save” button on those tabs for the values to actually be applied.
Without digging into code, it seems something changed with how values are saved/fetched from the DB.