Which browser, operating system and versions of those are you using?
OS
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.6 LTS
Release: 18.04
Codename: bionic
Chrome
$ google-chrome --version
Google Chrome 95.0.4638.69
WorldBrain's Memex extension version 3.0.5
Firefox
$ firefox -v
Mozilla Firefox 93.0
WorldBrain's Memex extension version 3.0.5
What are the steps you took that lead to the bug?
When I saw add-on update on Firefox I start cloud sync.
Result - pages synced successfully, but tags for a few pages not copied to Firefox.
After what I tried to create and delete tags in both browsers. Looks like only Firefox -> Chrome sync for tags working as expected.
Link to screen record - https://www.dropbox.com/s/73dcvh51ubuqvdi/out.ogv?dl=0