Please note, that right after wpForo 1.6.2 version release, we've also released wpForo Advanced Attachments addon new version for 1.6.2 compatibility. Before reporting the issue please follow to these steps:
1. Go to your dashboard plugins page and update wpForo and wpForo Advanced Attachments addon
2. Navigate to Dashboard > Forums > Settings > Addons and set Max Uploaded Size by Bytes. In latest version it's changed, so you can set it only by Bytes.
1 MB = 1048576 B
1 KB = 1024 B
3, Delete website cache again, then purge CDN, then delete all optimizer/minifier plugins caches again. Then navigate to website front-end and press Ctrl+F5 to reset browser cache, or just use incognito tab to test it.