In one of the project we used the following PowerShell CSOM code for creating managed metadata navigation terms in Sharepoint Online:
It worked successfully for many tenants but for one tenant it gave the following error:
Exception calling "ExecuteQuery" with "0" argument(s): "Term update failed because of save conflict."
Error appeared randomly, i.e. for the same sub site some time term has been created successfully and some time it failed with above error. There were no other changes so the reason was not in pending changes.
In order to avoid this error we applied the following workaround:
I.e. instead of single call to CreateTerm and ExecuteQuery we call it in the loop until call will be successful. Log showed that with this approach all navigation terms have been created properly at the end although for some sub sites it failed 1 time, for other 2 and for some even 3 times until it created term successfully, while for most of sub sites there were no errors at all. Hope that this engineering approach will help some one:).