I did raise a issue with CF about APO about it caching what it wasn’t supposed to cache, but it still does it. A large number of people on the s2member forum had the same issue. They stopped using APO,some stopped using Cloudflare!
As to the 524 - maybe its a coincidence, but 90 seconds after we turned it off (we had it on for a few days to see if it still did the cache thing) is when pages started timing out - and ONLY time out on that site. (only site with the CF plugin)
I am not a great believe in coincidence - turning that off was all we did -, but it’s possible something else broke at that same 2 minute interval.
Sid