The ServiceNow Securlet has been working without any issue for about 3 months, but it abruptly stops fetching new events.
The ServiceNow OAuth API issues refresh tokens with an 8640000 seconds (100 days) lifespan by default. As a result, the ServiceNow Securlet will not be able to fetch new information after the refresh token lifespan ends.
Deactivating and reactivating the ServiceNow Securlet can reset the refresh lifespan.
Additionally, the ServiceNow admin can set the Refresh Token Lifespan to a very large number to ensures the Refresh token does not expire every 100 days.