Bumping this exact thread. I provided a har file to support and was basically told it was the origin server causing the issue. When I grey cloud my customers site there are zero issues. This primarily occurs on cellular which makes sense due to latency and bandwidth, however I have 5G and get 300mb down on cellular and it still times out on Occassion. I will say its happened to their customers on ISP provided networks as well.
Anyone else experience what the thread linked above occurred. I tried page rules galore, bypassing a ton of different files, alternatively caching everything i can , etc. Nothing helped. Note that this is an insanely media , responsive web site. I see the 5xx in amplify ONLY when it goes through Cloudflare. when i grey cloud, poof, gone.