Users get double capabilities

FYI: All plugins and WP is on latest version.

If I change a subscriber to a custom role I created (which is the same as subscriber, but has one extra capability; priority_registration), then every user counts as 2.

Yesterday I did the first user and noticed this user had 2 (SQL) rows of wp_capabilities. When I deleted one the count was 1 (as expected).

I added 3 more users so now I have 4 priority users (1 of which I already fixed yesterday), but now the count was 6.

See this screenshot: https://imgur.com/a/ageW4

These users had double rows as well. I deleted them and the count was ok again.

I don’t think I added some custom code which could be related to this. Is this a known issue ?

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