When I open the Raid Manager, the box is a little out of the screen.
I tested it with Cache and WTF deleted and only this addon enabled.
Blizzard default:

EditModeExpanded enabled:

What happens if you enter Edit Mode and just drag it back into place?

To investigate, I need to see your:

1. Raid Manager settings
2. Party Frame settings
3. Raid Frame settings

Eg:

This should be re-opened.

Constantly with Edit Mode Expanded installed, my raid frames are either Vanished, Constantly opening to a blank page, or multiple other issues.

Changing it to not Clamp vs Clamp does not help. I've had to uninstall the addon as its far too distracting/broken. Re-installing it does not help, resetting does not help.

What do you have the raid frames / party frames attached to (if anything)?

Nothing at all. Default positions, using raid style for party, class colors enabled, default UI for both otherwise.

Sorry, not having any success recreating your issues. Its probably interference from another addon, but without any error messages I can't begin to work out which one.

I suggest you just disable the raid frame support in the addons options:

I'll show you what I tried:
https://i.imgur.com/RDbuS0i.mp4 (I can't upload it directly to Github)

I see, they made it a few pixels wider in a recent patch. Let me know if you still have issues.

With today's fix a new issue arose. Not sure if it can be marked as closed. I can also open a new issue if that's better.

The pop-out doesn't open, instead it converts to this half closed state, and if clicked again it disappears entirely.

Move it during edit mode after updating the addon then try again. The addon doesn't know if you saved the position while it was expanded or collapsed until after the update.

Seems to has fixed itself after a little wiggle. Thanks again and apologies for reopening unnecessarily. 👍

For what it's worth I've been having this issue myself for the past while, finally got around to reporting it. Since it isn't reproducable will try to figure out a cause.

Disabling the raid manager support didn't help, it just stayed where I put it and was open and blank. Tried resetting it, so far that seems to be working in very limited testing.

If you disable support, you need to /reload for anything to change

I was having same issue. After a long time trying to fix.... the answer is: You got edit it with it open and not closed. Also, can't use clamp to screen. I tried without any addons and using only editimode expanded.
Hope it gets improved on next builds.

I just don't know how you are all having these issues. It works fine when I move it while its closed.