Elise,
Thank you for your help, I see the number of requests for support you have, so I’d like to say that I appreciate your rapid feedback. Several points were solved by your answer (2, 3, 5, 6), please allow me to add some specifications for the few ones that weren’t (1 A&B, 4, 7).

1/ A/ Any clue about the reason for this behavior (it wasn’t like this at the beginning)?
1/ B/ Unfortunately this is unrelated (I increased this number indeed several times before going live while testing my site because I accidentally close the popup. Then I didn’t touch it for a long period when I launched my business, yet some customers reported they had to close the popup several times on a couple of hours time span, hence my question.) Edit : I just re-tested myself, see the screenshot attached: I just registered, got the green confirmation message after a very long while (~5-7 seconds) and the popup re-appeared immediately.

2/ That wasn’t the issue but it now seems resolved (I switched it to “scrolling” indeed after I saw that it was appearing immediately on mobile regardless on the “after x milliseconds” settings. I switched it back today to settings related to time, and it seems to work, I don’t know why.)

4/ Yep I saw this part, I was wondering if there was a simple way to affect the position and height of the popup on top of the width setting, maybe with a simple half line of code.

5/ Thank you I’ll try Add Rule > Custom Selectors

6/ I’ll try that too.

7/ Any clue?