[Flathub] Cannot launch second window of LibreWolf, getting error

I've downgraded back to LibreWolf 93.0 from LibreWolf 94.0 due to an issue affecting the launching of a second instance of LibreWolf.

sudo flatpak update \
  --commit=fbdb6b9d8be4016b8f715f1fb8b395bcb240c508512ea4a2f63c8577f91d2fd9 \
  io.gitlab.librewolf-community

I was running LibreWolf 94.0 on Xubuntu 20.04. I startup LibreWolf and it runs okay, but when I click on the LibreWolf launcher on my panel to get second LibreWolf window running, I'm got this error:

LibreWolf is already running, but is not responding. To use LibreWolf, you must first close the existing LibreWolf process, restart your device, or use a different profile.

To see what's happening under the hood, I ran LibreWolf in the Terminal and these are the results:

I was able to run LibreWolf from the Terminal:

~$ flatpak run io.gitlab.librewolf-community
ATTENTION: default value of option mesa_glthread overridden by environment.
ATTENTION: default value of option mesa_glthread overridden by environment.
ATTENTION: default value of option mesa_glthread overridden by environment.
ATTENTION: default value of option mesa_glthread overridden by environment.
JavaScript error: resource://gre/modules/PromiseWorker.jsm, line 106: Error: Could not get children of file(/home/RagglenLove/.var/app/io.gitlab.librewolf-community/cache/librewolf/xxxxxxxx.default-release/thumbnails) because it does not exist
JavaScript error: moz-extension://5793ff7d-2782-4a84-a020-41d927b33efb/lib/main.js, line 306: Error: Could not establish connection. Receiving end does not exist.
JavaScript error: undefined, line 0: Error: Content script already unregistered
JavaScript error: undefined, line 0: Error: Content script already unregistered
JavaScript error: undefined, line 0: Error: Content script already unregistered
JavaScript error: undefined, line 0: Error: Content script already unregistered
JavaScript error: moz-extension://5793ff7d-2782-4a84-a020-41d927b33efb/lib/main.js, line 306: Error: Could not establish connection. Receiving end does not exist.

I opened another Terminal window and tried to launch second instance of LibreWolf, this is what happened.

The "LibreWolf is already running, but is not responding" error appears and this is the Terminal result:

~$ flatpak run io.gitlab.librewolf-community
ATTENTION: default value of option mesa_glthread overridden by environment.
ATTENTION: default value of option mesa_glthread overridden by environment.
ATTENTION: default value of option mesa_glthread overridden by environment.
ATTENTION: default value of option mesa_glthread overridden by environment.
JavaScript error: resource://gre/modules/XULStore.jsm, line 66: Error: Can't find profile directory.
JavaScript error: resource://gre/modules/XULStore.jsm, line 66: Error: Can't find profile directory.
JavaScript error: resource://gre/modules/XULStore.jsm, line 66: Error: Can't find profile directory.
JavaScript error: resource://gre/modules/XULStore.jsm, line 66: Error: Can't find profile directory.
JavaScript error: resource://gre/modules/XULStore.jsm, line 66: Error: Can't find profile directory.

I've downgraded back to LibreWolf 93.0 and the issue was fixed, so this is a problem with LibreWolf 94.0.

I've also reported this here: https://github.com/flathub/io.gitlab.librewolf-community/issues/6