Some more findings :
1.Tested my setup with 9.1.502 on a RPI 3B (with rpi2 dist) , no problem with picture viewing and no freezes so far.
I guess its indeed only problem with RPI4 dist.
2.When enabling debug logging the memory usage on the OSD drop much more when viewing to attached jpg on the RPI4.
On RPI4 it drops like 50-60mb and then goes back up (if its not get freezed).
On RPI3B same pictures drops like 5-15 mb and goes back up. (and no UI freeze so far)
Its indeed problem with certain jpg types which also cause problem with some thumb nails.
Let me know if anything else is needed.