Here is a quick workaround for avoiding the new 4.18 Editor Freeze with “Updating References” when editing Levels that are referenced by 2 other Levels, Sequences or other assets.
Instead of Deleting an Actor and triggering the Freeze, you can quickly drag it into any Sequence, “Convert to Spawnable”, and delete it there! This uses one Bug to avoid another Bug. The new Soft/Cross Level Reference enforcement system in 4.18 is broken. It is triggered every time you Delete, Rename or Cut an Actor in a Level that is referenced by 2 other external assets. It is triggered even if you abort the dialog about reference updates, leading to an Editor Freeze and requiring a Force Close and lost work. The new trigger is supposed to update the external Soft References to the new name or deletion, but instead hangs when it encounters 2 of them. However, the Sequencer “Convert to Spawnable” has not yet implemented this trigger when it removes the actor, which is finally a useful bug!
Unfortunately, for Renaming the Actors, you have to resort to much slower Renaming the Referenced Level so it temporarily escapes this broken new system. You have to be careful Not to Save all the assets that will now get dirtied and updated with the new Level name. After your edits, you can save the edited Level, and be sure to use “Fix up Redirectors in Folder” in its folder, because there is a hidden link asset there now with the old name, and this will remove it. Then, you can rename it back to the old name. You can either Restart the Editor, or Asset Actions/Reload to restore all the dirtied assets from the temporary name.
It’s all a big colossal mess, but such seems to be the future of Unreal development while a better engine comes along… 