Do you use the dbLocalizationProvider?
If yes, then upgrade to newest version. See this thread: https://world.episerver.com/forum/developer-forum/-Episerver-75-CMS/Thread-Container/2019/10/takes-a-lot-of-time-for-epi-cms-resources-to-load-on-dxc-service/
I know it says dxc, but it happens on-prem too
Our client reported that using the EPiServer CMS is slow. I looked into it and noticed that when opening the CMS about 1000 files are being loaded by the dojo.js. This is causing so much overhead that it takes about half a minute before the CMS loads.
Is there maybe a way to bundle these files to reduce the overhead and make the cms load faster?
Also all the files are uncompressed while we have this in our Web.config:
<clientResources debug="false" />
Are there other ways to speed up the CMS?
We are using the latest episerver version 126.96.36.199