I have Map1 with a zoom level of 3 and I have a Map1 with zoom level of 4.
When I lock the Map1 Lvl3 it also locks the Map1 Lvl4.

I then travel around 1000 Blocks to another base where I have the same Map1 lvl 4 duplicated in an item frame and this one was locked as well.

Second test:
I then have locked Map2 Level 0, and all other Map2 Level 1+2+3+4 were locked as well.

I don't know yet if it has to do that they have the same name or if they were all cloned from the same 2 maps. (Map1 and Map2)
I also play a very old World but the maps were made in 1.18, 1.19.

I could upload my world but it's 100 Mb.

Update:

Renaming a map doesn't prevent the issue - I think it's related that they were cloned from the same "base" map.

I also found that the higher level map doesn't really get locked, it just says so in the tooltip and in the cartography table it's not possible to lock it with a glass pane. (No recipe as if the map would be already locked)

However the map can be updated by discovering new areas, or when the world blocks changes.