Not recently, but over the last few months I have seen that and other error messages when trying to access Forum.
I was blaming my Linux OS up grades, but not conclusive and also "cloudflare".
These are a bit tricky, as there is nothing in the error log - so not really much to go on.
The site is monitored every minute, so if it stays down longer than 3 minutes (3 down times in a row) - that's when my phone goes nuts and sends me scuttling for a computer to sort it out.
Ignores my phone's silent setting too - so even if it's silly o clock in the morning, I'll still get it!
This only does monitor the homepage though, so if for some reason another random page (and only that page) breaks, I won't know unless one of you wonderful people alert me