In out of box instance, when there is a conflicting change request, if planned start and end date are modified so that it does not conflict anymore, the other change request does not update the conflict status until 'Check Conflicts' is manually clicked.

Configuration :

1. Create a normal change with a Configuration Item as A and planned start and end dates as 01/01/2021 11AM to 01/31/2021 11AM.
2.Notice that the Conflict status on this shows as No conflict.
3. Now create another Normal change with the same configuration item and planned start and end dates as 01/01/2021 11AM to 01/21/2021 11AM which means it is scheduled to run between the times of the first one.
4.Once the second change request is saved, the Conflict status on the first one automatically updates to Conflict and even on the second one the Conflict status shows conflict which is expected.
5. Now change the planned start and end dates on the second one to 02/01/2021 11AM to 02/25/2021 11AM which means the schedule for this second one does not conflict with the first one and save the record.
6. The Conflict status on the second one updates to No conflict.
7. On the first one the conflict status still shows 'Conflict' and you will need to use the related link named 'Check Conflict' for this to run and update the first change request.

This is expected functionality currently. It is intentional that the Conflict check will not be run on the related change automatically.

An enhancement can be created if they would like to dynamically update the conflict status when changes are made to existing change requests following the process in the below knowledge article :

https://hi.service-now.com/kb_view.do?sysparm_article=KB0755878