It finally finished..
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While I was waiting, I looked at pvecm status and found out it thought I had 4 nodes (see expected votes), when I only have 2 nodes.

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I used pvecm expected 2 on both and suddenly the updates moved on and I was able to log in to the web interface immediately.
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In the web interface, it showed a pve3 and pve4. These were some test setups I did months ago.
I deleted the nodes from the CLI and everything looks clean again.
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