Jira Cloud for Sheets might fail with the error Hmmm ... looks like we stumbled a bit, please try again or contact Atlassian support if the issue persists. (§GS-404).
That happens because the integration is unable to find the target sheet.
There are no clear steps that could lead to replicating that problem that have been identified yet.
The integration will be able to load content on the sheet.
The integration simply fails to load content on the target sheet.
Recreating the affected sheet normally resolves the problem.