I'm using almost current MyBB forum software to deliver a page containing 100 jpg images. Up to 3/30/19, I had no problems with this at all. My domain is not a high traffic forum. On that day, pages started to come back with broken images. Browser tools show 503 and 507 errors. A refresh will deliver a different set of some images with others errored out.
I can retrieve the entire page properly if I force the browser to make HTTP/1.1 fetches.
Support says it is my content, not their server. I disagree. I have verified site files, and nothing has changed. Any ideas?
It turns out the Expand Business Hosting server is not capable of delivering pages with high number of attachments. All attachments are delivered through a database query, and the MySQL database was choking on the shared server environment. Memory usage was quite high, free memory was very low, there was no way to flush cached memory. The server was the wrong platform under HTTP2.