Hi!
I reproduced it.
1. Make some write load on master: `pgbench -i -s 100000 testdb`
2. On sync replica drop output connections, while pgbench init database: `ip6tables -A OUTPUT -p tcp --dport 5432 -j DROP`
3. Until was_sender_timeout reached, i send SIGHUB on master: `select pg_reload_conf();`
After that walsender forever stay in WaitEventSetWait, because no timeout
src/backend/libpq/be-secure.c:273
WaitEventSetWait(FeBeWaitSet, -1 /* no timeout */ , &event, 1,
WAIT_EVENT_CLIENT_READ);