Used to work, Xcode 14b4 now doesn't: Actor-isolated property 'lastLoggedTimestamp' can not be mutated from a Sendable closure

Yesterday I was running with Xcode 13.4.1 and 14b3, and this line of code was fine. I just installed Xcode 14b4 and I now get this error:

await furnace.lastLoggedTimestamp = transients.timestamp
MeasurementLogger.swift:92:23: error build: Actor-isolated property 'lastLoggedTimestamp' can not be mutated from a Sendable closure
Mutation of this property is only permitted within the actor

This seems like an odd change to have from beta 3 to beta 4. Is this a new bug or was it a bug before?

Can you share more context of this bug?