Apple Watch forgets time, activity and more when far from iPhone

Hi all,

Bought an Apple Watch SE for the first time last week. It already happened two times that the watch completely forgets what time is it, my previous activity and even the connection to my iPhone.

Both times this happened when my iPhone was far from the watch for a long time (one time an entire night where the phone was left on airplane mode, the other forgot the watch at home charging for 3h).

Is this normal or is there anything that I'm not seeing?

As for extra information, in case it's needed, when I enter the activity app it does the onboarding of first time use and when I ask the watch to find my phone it says "Pinging Iphone" without doing anything.

Thanks for your help!