We've upgraded our BlueOcean plugins to the latest 1.15.0 and restarted Jenkins.
Afterward, we were unable to access the `activity` tab and some of the builds. 
Initially we thought it was a browser issue, but after doing a curl request we noticed it's not working as well:

$ time curl -I https://domain.com/blue/organizations/jenkins/project%2FjobName/detail/master/2217/pipeline/
^C
real 3m53,812s
user 0m0,010s
sys 0m0,008s

There are no exception logs in Jenkins which can point to what's causing this.
However I did make a thread dump which I've attached. 

I wasn't sure which component this relates to exactly so I've marked `core`.