100% CPU usage on webtunnel bridges since 0.4.8.20

Hi

Since the 0.4.8.20 update Tor uses 100% CPU on webtunnel bridges.

I have the problem on my bridge and another two people from #tor-relay reported the same issue and today there was another one on the forum

The issue also persists on .21. Relays or obfs4 does not seem to be affected.