Massively increased load times

Hi!

Great plugin but I'm having an issue with performance. Read similar issues like mine, none of them gave me the needed answer. In most of them it's assumed that there's a conflict with another plugin or theme. Tried to debug it, disable all the plugins except essential ones, switched to default WP theme, sadly it didn't help.

I've created two copies of the website with minimal functionality to show the problem. There's a mobile app which is getting data from the website so the main target is REST API endpoints. Both of these copies are in the same server and the setup is also identical except for the plugin in question.

Several examples:

http://s3-disabled.invsbl.lt/wp-json/app/v2/pois 4-5s load time
https://s3.invsbl.lt/wp-json/app/v2/pois 22-26s load time

http://s3-disabled.invsbl.lt/wp-json/app/v2/routes 1-2s load time
https://s3.invsbl.lt/wp-json/app/v2/routes 4-5s load time

There are 3 plugins enabled in s3 version: https://nimb.ws/WBon7l

ACF, S3 and our custom plugin which inits CPTs, creates endpoints and uses ACF functions to expose data. No optimisations, anything with file directories, just common ACF functions.

This plugin is working great apart from performance problem so it would be awesome to find the problem but I'm unable to do that. Do you have any idea what might be wrong?

Thanks a lot.

Similar issues:

https://github.com/humanmade/S3-Uploads/issues/148
https://github.com/humanmade/S3-Uploads/issues/520
https://github.com/humanmade/S3-Uploads/issues/466
https://github.com/humanmade/S3-Uploads/issues/395
https://github.com/humanmade/S3-Uploads/issues/350
https://github.com/humanmade/S3-Uploads/issues/431

Start with the REST API endpoints /wp-json/app/v2/pois and /wp-json/app/v2/routes, comparing the S3-enabled and S3-disabled site copies under the same server setup. Profile the requests and the three enabled plugins to isolate the performance difference; done means identifying a reproducible S3-Uploads-related cause and documenting the evidence.

Written by the indexing model from the issue text.