With the"Attributes" command you can change the layer of multiple entities in one go. You also can combine single pick and window selection, though a bit tricky as I just have found out.
There are several situations where after an operation something seems disappeared and Auto Zoom brings it back. So that's always worth a try.
I always fear to have to deal with blocks issues. I don't know if it's a lack of understanding or really buggy or not well implemented. Any way I don't understand completely what is going on, there also seems to be some block and layer interaction, what happens when there is a block within a block, ...I'm not much of a help here. But will I try out the procedures you have described.
LibreCAD is maintained and developed, but progress is slow. If someone makes a contribution it is mainly something that person feels it needs it for it's own interest. Issues of common welfare thus are neglected.
Generally the hype is for 3d design (3d printing!), simple 2d-drawings is for oldies.
dellus