Recently I saw some strange behaviour of a Teensy 4.1 with Ethernet, both PSRAMs and MicroSD.
No overclock, nothing else connected to the 3.3V rail.
During heavy data processing and transmission, it sporadically rebooted, without any cause in the code.

The casue was the voltage regulator as I've found with a transient recorder and a FLIR! It began to build up heat very slowly and suddenly switched off the Teensy 4.1 for a fraction of a second, before starting up again for a varying span of time, minutes to about an hour, before it turned off again. When the code is more idle or there is less network traffic or less SD operatios, this does not happen.

When it happens during write, the SD filesystem gets shattered. This is with different types of SD, all real SanDisk, so the SD is not the fault. There is not enough buffering capacity to allow the SD to finish block operations, before power dies.

So the voltage regulator is at it's full maximum, or even beyond, if Teensy 4.1 is equipped with all it's possible features and working, even without any peripheral connected to 3.3V.

I suggest to design a better voltage regulator on the next Teensy!