“P3 has not detected any opcode optimizers on your site. Although none were detected, an opcode optimizer may still be present. Contact your server administrator with any questions.”
I’m using a VPS server, Linux-based, PHP is updated.
no drop-ins that I know of (how can I find out which ones I have?)
I was using W3 cache plugin, but I deleted it and removed all cache files from the server when I first ran into this issue.
One thing I noticed was that if I click Advanced Settings, I can check the boxes for Use my IP address, Attempt to disable opcode optimizers, and Attempt to circumvent browser cache. I can then run the scan properly. However, if I click Advanced Settings link again, the boxes are unchecked again.