Did you manage to yet?
The site is unstable and I personally recommend against touching your lists right now. This could be one of two things:
1) You deleted it and it was automatically recovered as the devs have been recovering stuff as long it was ever at one point added to your lists. (They have been recovering even deleted works + works that have been deleted off the site to people's lists)
2) Your end and the sever are not communicating. Any change you make isn't properly reflected by the server immediately. You may need to make a change, then wait a minute to see if the change was reflected or try again.
Or it may be a 3rd reason that only the devs know
FAQ here in case
https://www.mangago.me/home/mangatopic/21255174/
I've been going through almost every message I've replied to make a timeline, and I just realised I might've answered your question wrong!
If you meant these lists: https://www.mangago.me/home/people/4709660/list/
Then it should be safe. The site must've just had issues with not updating data.
Though I am curious, do you remember how many times you tried to delete it back then?
I tried at least 5 times a day for about 2 weeks. I was so embarrassed to have those manwhas in my list that I wanted to get rid of them as soon as possible. Luckily, I was able to do so today! And even though you gave the me wrong info, It did help me a lot so thank you anyways. (Sorry for taking so long to answer, last week was exam season)

Hiii, I have been trying to delete this one manwha from my romance list and is not letting me, could somebody please help me? (▰˘◡˘▰)