@nekr0z I'm curious if you may have blocked incoming webmentions from micro.blog in webmention.io? (I've accidentally done it once or twice for other domains.) Look at: webmention.io/settings/... to see if that's the root of your issue. I have my own stand-alone WordPress site and frequently get webmentions from micro.blog. Here's an example: https://boffosocko.com/2020/04/25/55770533/#comment-285985.
I also frequently reply to others on micro.blog without issues, though depending on how they set their preferences, micro.blog sites have the choice of either showing or not showing Webmentions. (And this is a relatively new feature that's supported in the past few months.)
If you're having issues on the back-and-forth, you should definitely ping @manton, who I've always found to be incredibly helpful.
I rarely visit micro.blog on the web since I read all of the sites I'm following on it either individually in my feed reader or in aggregate using the feed: micro.blog/feeds/c.j... (You can get yours by replacing the "c" with your username. I'll also mention that Inoreader pushed some changes for titleless posts in December that makes the presentation of feeds from micro.blog much better than most other feed readers.) Since all the comments on my posts come back to me as webmentions, I never really need to visit its site other than occasional visits to the "discover" tabs to see things that don't make my personal feed.