It helps to install a physical SIM card
The problem manifests itself on the sim cards of various operators. According to Apple smartphone owners, iMessage and FaceTime are randomly deactivated and there is no way to reactivate them. The only solution is to get a physical SIM card.
Many users complain about the same thing or cannot activate iMessage and FaceTime at all. For some, this solution worked: either deactivate and reactivate the eSIM, or activate a new one.
The problem was noticed at least in iOS 15.4. Apple has not yet responded to the complaints.
Recall that eSIM is a form of programmable SIM card that is built directly into the device.