In 25.2.28 did we make any changes to how the jmeter agent behaves? Getting a Checkpoint Error 503.
There was no change in the jmeter behavior. The capacity is always an estimate. In case of an error, the monitors may start timing out, the time when agents are busy gets longer and the capacity may not be sufficient any more. Try raising the number of jmeter agents by 10-30%. If they hit the limit in the future,then raise it even more
The number of IP addresses should not be an issue.