Accidentally upgraded to 4 stable from 3, http binding not working

It was not enough threads, had to modify /etc/openhab/services/runtime.cfg and add:

org.openhab.webclient:minThreadsShared=10
org.openhab.webclient:maxThreadsShared=40
org.openhab.webclient:minThreadsCustom=10
org.openhab.webclient:maxThreadsCustom=20

Found solution here: