I'm having the same issue in CM 23.4 patch 1 - I've logged a ticket with OpenText, hopefully the underlying issue can be fixed...

We've had this become more frequent recently (last few months) with 9.4. Will be following this to see if anyone finds a solution!

Interestingly we had similar today ..... 9.4 (2.602) from memory.

Following for more info, fingers crossed

I don't have an outright answer to your questions, just some observations based on our experiences with multiple integrations.  The first I will point out is that long searches - especially where a sort or wide searching can result in APIs going long in its response.  In order to know why API performance is sluggish or non-responsive a deeper dive through a tool like Dynatrace would be necessary.  In one particular case, we found that an API was acting up based on a search that did a high number of records with matching criteria and then sort.  This is also a long request in the rich client.  Perhaps asking your developers what kinds of calls they are doing will help in your diagnostics?  Dynatrace was able to give us clues on what was happening in this case.  It also showed us periods in which user frustration and response times were high. 

Another issue I've observed is any kind of wide batch processing - like a database true up, where an API will hammer us with requests over multiple connections would cause an obvious decrease in performance.  Without discussing the actual processes with the CM API, your developers can do unexpected calls that could be done in more efficient manner.  For example,  the dev wanted to see what records were deleted - so guess what? At 2 AM on a Sunday they decided to download the entire collection's data - where the more efficient effort would have been looking at the audit log searching for URIs that matched their database for deletion events.