Pages not caching – conflict with EWWW Image Optimiser

I had an odd issue where pages were not prebuilding.

Upon reviewing the error logs, I found that EWWWW was causing issues (PHP Fatal error: print_r(): Cannot use output buffering in output buffering display handlers in /*Removed Directory Names*/plugins/ewww-image-optimizer/classes/class-ewww-image.php on line 173).

Upon disabling it, pre-build starting working immediately. I would assume it would be down to EWWWW to fix on their side.

Just posting this as an FYI for anyone else that stumbles upon this issue.