I’d start by checking what the Create Issue action is actually receiving at runtime. The error suggests the action isn't getting a valid value for PTask Number, even though the data pill looks populated in Flow Designer.

I've seen cases where a pill displays a value, but resolves to null or an unexpected object when the flow executes, which can trigger the "Could not deserialize value from sys_flow_value sys_id" error.

As a quick test, try hardcoding a valid PTask number in the Create Issue action. If that works, the issue is likely with the data pill mapping rather than Jira itself.Also check the Flow Execution Details and inspect the inputs passed to the Jira action. I'd be interested to see whether the action is receiving the actual PTask number or a record/sys_id reference instead.

Since you mentioned this was working previously and nothing has changed in the flow, it's also worth checking whether there were any recent platform or Jira Spoke updates that could have affected input validation.