Unfortunately I don’t have this much experience or knowledge.
Personally I am only able to do basic installing and updates but to troubleshoot, I cannot.
My expectation is that the developers will be taking a look into what bug has appeared and provide an immediate fix considering it has completely halted our business operations.
LATE EDIT: So I am running two ERPNext on the same server and one is working properly, the second has this issue with saving the calendar events.
If I reinstall erpnext will it delete all the information in it ?
If you are running two sites on the same server then both sites should either work or not work. From /frappe-bench/ folder
run
bench version
and post results
So I have managed to fix it but I can’t say where the problem was coming from.
To be as specific as possible, I had to restart supervisor 2-3 times and then the problem went away.
However, I am very sure there is a problem with the calendar events because since forever using erpnext when you choose a start and end date for the event, the end date of the event does not get saved. I have to clear the cache and refresh the page to be able to set the end date of the event… this is another issue.