It's happened to me quite a few times, though I don't experience it as much myself. Lotro is a pretty old game, so characters freezing and disconnections is a common thing, unfortunately. There's nothing that can really prevent this problem from happening, but there is a way to get past it, when it happens.
Alt + Tabbing out of the game and forcefully shutting it down always works for me to get my character unstuck. I never even wait to get the black screen anymore, takes too much time, and I know it'll give me the error anyway. When I get stuck in place and can't move, I just immediately alt + Tab out of my game, forcefully shut the game down by right-clicking it's icon in my taskbar at the bottom of the screen and selecting to close the game, then load into it again. It usually gives me the error that my connection was lost before I can fully load in to the main menu, then boots me out again, but every time I then load in the second time, it lets me in, with my character not being frozen anymore, and my progress still there. This is a faster progress than waiting for the black screen and the error to boot you out.

Best thing to do when this happens it just shut down the game down then load back in again. If it doesn't let you alt + Tab out of the game, then it's better to just hard restart your computer.

Same problem

Is there any chance buried in your internet settings is a 'play / online timer'? I can't remember the game my wife used to play, but in the settings I could limit how long she could be online.

(she's the type that gets obsessed and doesn't know when to take a break)

hard to track down cause of these disconnects. this happened to me in another game for over 6 months yet this game worked fine. many emails to tech support. many calls to ISP. nothing solved the problem. then someone at the ISP noticed that others in my neighborhood were having the same issue. turned out replacing the network box in the neighborhood that we were all connected to resolved the problem. there was nothing wrong with the game servers, game software, my computer settings, or my router.

if you have a laptop, getting disconnects when you play elsewhere?
have access to another computer where you play? see if problem occurs on that one also
have a friend with a laptop? see if the same thing happens when playing on their machine at your place.