Cannot follow Person who's following me and I followed once

Ok, well.
I reportet this problem once and I thought it was fixed, but it isn't.
So:

I just want to follow one person.
I followed this person before.
This person followes me.
Someday, I didn't follow this person any more- without doing anything.
Now, when I want to follow this person, the message pops up "Something went wrong. Please refresh the page and try again!"
Don't think I didn't tried again after refreshing (hundreds of times I tried)

I also tried to type "follow person_x". The Message came, that all would be fine. But it still wasn't.

Now, guys, I REALLY want to follow this person.
I can follow anybody else, I know. But I want THIS special person.

Tell me: What can I do?
Otherwise: What can YOU do for me?

DM to me for advice! :)

Thanks for your patience and your help!

Sincerly
biti