I noticed the following to be in /var/lib/openhab2/etc/org.ops4j.pax.logging.cfg.dpkg-dist.
I (as probably you as well) refused to have the install routine replace my org.ops4j.pax.logging.cfg.
# Filters warnings about small thread pools.
# The thread pool is kept small intentionally for supporting resource constrained hardware.
log4j2.logger.threadpoolbudget.name = org.eclipse.jetty.util.thread.ThreadPoolBudget
log4j2.logger.threadpoolbudget.level = ERROR