I recently changed these value in cPanel for php (no manual file edit, jut using the build in configuration option). Saved and rebooted.
memory_limit = 512
max_execution_time = 120
max_input_time = 120
upload_max_filesize = 128
I've done this before and there has never been any ill affect (ever). But now when you upload an avatar, XenForo says, "upload complete", but nothing shows.
When you try to upload a file in a thread it appears as though it is uploaded, but you have no options.
I cannot imagine how those settings could negatively affect this. And there is no error messages or anything in the logs.