Unable to block someone on my instagram

Hello,

I've been trying in vain for a few days to block someone on Instagram, but I can't do it anymore. Let me explain, throughout the year I've blocked and unblocked this person several times without any problem, but now it's been three times (once last month and twice yesterday and today) that I've tried to block this person, but it's impossible. I go to their page, I click on block, so far everything is going normally, I see the profile turn into (blocked with 0 following and 0 followers) and the little notification below tells me that this person has indeed been blocked, but then it gets weird. Indeed, this person should logically end up on the list of blocked users, and I should also be able to find them when I type their name in the search bar, but nothing works, they are nowhere to be found. At first, I thought they blocked me at the moment I did it and that this happened in just a few milliseconds. This morning, when I typed their first name in the search bar, this person is visible again, and I see that when I click on their profile, the "unblock" option appears by itself without me doing anything—I don't understand at all. So I went through the same blocking process again, and once again, poof, total disappearance as if they had blocked me, but that's impossible at this hour; this person works without their phone, and twice in a row at the same second would not be possible. I imagine that tomorrow I will find them again unblocked in my search bar. I don't understand at all; however, I waited a month between the two attempts to make sure it wasn't Instagram preventing me from blocking this person, perhaps due to blocking and unblocking them too many times in a year (please, no judgment, you don't know the reasons). So I would like to know if anyone else has had the same issue and how to ensure that this person is really blocked. I also wonder if they might have hacked my Instagram or set something up so that I can't block them. Finally, I am open to any explanations or tips regarding this. Thank you and have a good day.