Same here, happens frequently with LTE enabled, with good signal, on an Irish SIM (slot #2) while in Spain. Most times while in my pocket.
Slot #1 has a Spanish SIM.
Disabling LTE seems to prevent issue.
Bottom module was replaced months ago… AFAIK it only affects charging not running from battery.
LTE can be power hungry so I am suspecting an issue with the power circuit.
Maybe a bigger stabilizing capacitor would help…