Sudden slow load of oc.js

I’m running Nextcloud in Docker with a swag reverse proxy on an unraid server and the performance has seriously degraded over the past few weeks. I’ve run some diagnostics using and it’s showing 45s wait on oc.js

Nextcloud’s own Security & setup warnings section shows no errors and I’m running 20.0.4.

Not sure if this is a reverse proxy issue or a nextcloud issue - any guidance grateful received. Thank you.