Hotfix is deployed on our side. 
As noted above, if an event comes in with an unreasonably old timestamp, this will replace that with the current timestamp at the time of event arrival.
Sidenote for State Stays Rules (tap to expand)
In all practicality, this shouldn’t have any major implications, but it’s possible that it could impact certain ‘state-stays’ conditions in rules depending on atomic time float between SmartThings servers and ours. Ideally we’ll see SmartThings fix things on their side shortly and the system will automatically use their timestamps without any further action required.