Bug with difficult words leads to broken session

I think these are the same words that I have ticked manually as difficult so I can go over them again.
I did that from the page that you get after a mistake / see answer click.
I also got other difficult words automatically in the same session for a total of 15-19 words.
And then I did two review sessions for difficult words with 100% completion rate.
In the end 10 words in my difficult words list didn’t get cleared.
So I went and unchecked them manually.
Now I get “Could not load session. Sorry” every time when I click the difficult words exercise.
Tried login/logout and it doesn’t help.
German 1 course. Part 14.
I think it’s best not to use memrise to give you a chance to debug it while it’s still reproducing.

Update:
The problem resolved on its own after some time.
I haven’t done any exercises in the mean time.

I very often get the “Whoops. Could not load the session. Sorry.” pop-up when I click on the “Difficult words” button. I think it’s because I either reviewed those words and they should have been cleared, or I manually unchecked them, but for some reason, my home page still shows that I have some difficult words to study, while I actually haven’t. Hence when you click the button, no words are found

EDIT : I actually now have two phantom difficult words which are permanently stuck in Spanish 1 ! My dashboard keeps showing that I have (at least) two difficult words, but it’s impossible to review them

I have the same

From the app, difficult words is greyed out.

From the web (chrome) difficult words shows one item but when clicking on it I get the error:

Could not load the session. Sorry.

This is the error from chrome:

raven.js:1483 GET https://www.memrise.com/ajax/session/?course_id=2022170&course_slug=german-1-98&session_slug=difficult_words&_=1560729685823 400

Can anyone help?

Tried signing in and out
Checking on the iOS app (iOS app doesn’t show difficult words count even if browser is showing a count)
tried different browsers, firefox, nightly, iexplore, all showing the same behaviour

the 400 error would suggest this is server side?

Looks like the dash is stuck with a value for difficult words enabling the button but when clicked there is nothing in there. If a new difficult word is added the session loads but only new words are accessible however the difficult words count keeps rising

if you’re experiencing this bug can you reply below please

thanks