In my case the card shows up only when is not hot (so every second reboot).
But! Recently I put inside my omnia old notebook fan (just because I can there was no other reason) and what a surprise - my 5G radio is working like a charm. Then due to the noise from fan I removed it and my 5G was the same - not booting up when hot. As a compromise I removed radio top cover and attached my old raspberry pi passive cooler. It works great and in 99% the card shows up after reboot except cases when the card was intensively used before reboot (like maxed oud by iperf).
[passive cooling - not actual photo later changed to slighty bigger block]
According manufacturer spec. the card operating temperature is -20ºC to 70ºC (https://www.compex.com.sg/product/wle900vx/) but industrial grade version should work up to 90° (https://www.compex.com.sg/product/wle900vx-industrial-grade/).
Considering board temperature of omnia somewhere between 60°-90° and heating of 5G itself I think that some cards might be on the edge of reliability so bit of cooling can help like in my case.
Anyway I ordered already this beast https://www.compex.com.sg/product/wle1216v5-20/ so I hope it will work better.