Hello,
Thanks to the help of one rig owner, we discovered that a pool recently used on Betarigs (cryptovein.com) was using an uncommon and undocumented stratum command that had a bad side effect.
This had the effect of making the rigs reconnect to another stratum server, completely bypassing Betarigs. Because of that, the mining was never stopped.
So this explains why in Betarigs, it was stuck in "Ends in a few moments" -- we display this label when we do not see the rig anymore, and we weren't seeing the rig anymore, since it was bypassing Betarigs.
This could not have been exploited by customers, as the credentials used on the reconnected stratum servers were the rig owner betarigs credentials. So the customers are not credited with the mining on the reconnected stratum server.
This is now fixed, and for the affected cgminers still mining after end of rental, you just need to reboot them. We have identified 7 rigs affected by this.