I wonder if this is caused by timeouts?  

I'm thinking that, but hard to prove sort of thing. It's a brand new server as well (assuming it's hosted) but I'm not seeing wither the Apps server or the SQL server being hammered though. 

As it is 2022 I'm going to check through the release notes for 2023 in case something is mentioned as I know there is an issue with 2022 about the number of SQL connections. 

The customer had way less RAM on the SQL Server than we would have recommended. Got them to increase it and all issues went away. (Don't know how that escaped the checks)

Was that showing as a timeout anywhere?

Not really, but having it work on showing some dashboard gadgets and not others. Only to change when you refresh the screen made me think about it having to run all the queries. 

SQL Server was only 16Gb and SQL was restricted in it to 10Gb (this also houses the Sage 200 databases as well). Server since updated to have 32Gb and SQL restricted to 26Gb and now it's much smoother.