Loss of 5G

This is most likely a power saving ‘feature’ is/where 4G LTE + 5G exist.

5G can/does require more processing due to higher order of signal modulation and an attempt to keep the noise floor low.   Due to TANSTAAFL (there ain’t no such thing as a free lunch), more processing power required for cleaner signal/lower noise/wider channels/more forms of carrier aggregation

Recall the old days of a flip phone which could be on standby for +1 week on GSM.  If it had today’s battery, it might sit idle for a month.

https://support.google.com/pixelphone/answer/2819583?sjid=4502716063295003806-NA#adaptive_connectivity&zippy=%2Cadaptive-connectivity-pixel-a-g-later