dazinism Today I set the "Preferred Network Type" (Settings - Network & Internet - Internet - click the gear icon next to your network operator name - Preferred Network Type) to LTE. Before it was set to "5G (recommended).
With the 5G setting I have only seen LTE written next to the mobile signal symbol, and as far as I know LTE is a 4G technology. I also checked now and on the operator map the region where I am should be covered by 5G, but I have never seen 5G next to the mobile signal symbol. Looking further into this, it looks like the 5G is a paid option with my operator, which I do not have, so LTE is the maximum I can get anyway.
As I have set the LTE preferred network type only today, I will need a few days though to see if this setting solves the issue. After setting the LTE I still had this issue once and that it why I mention in my original message that it also happened on LTE, but it actually only happened once, so one occurrence is not really relevant.