Non-fatal assertion !(entry == NULL) failed in dos_new_client_conn at ../src/core/or/dos.c:706

Summary

Running the latest tor relay code causes occasional stacktraces

Steps to reproduce:

adapt torrc, run torclient and wait for the stacktrace to show up.

Environment

tor v4.5.7
Linux Ubuntu Focal (kernel 5.4.0-1038-oracle #41-Ubuntu SMP x86_64)
using apt for installation/updates with following source file entry:
deb     [arch=amd64] https://deb.torproject.org/torproject.org focal main
deb-src [arch=amd64] https://deb.torproject.org/torproject.org focal main

Relevant logs and/or screenshots

Bug: Tor 0.4.5.7: Non-fatal assertion !(entry == NULL) failed in dos_new_client_conn at ../src/core/or/dos.c:706. Stack trace: (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(log_backtrace_impl+0x5a) [0x55ed2d79ce7a] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(tor_bug_occurred_+0x16f) [0x55ed2d7a828f] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(channel_do_open_actions+0x1b7) [0x55ed2d800477] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(channel_change_state_open+0x2e) [0x55ed2d8004fe] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(channel_tls_handle_state_change_on_orconn+0xb2) [0x55ed2d8056a2] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(connection_or_set_state_open+0x26) [0x55ed2d84e226] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(channel_tls_handle_cell+0x1a2) [0x55ed2d805962] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(+0x19fcdc) [0x55ed2d84acdc] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(connection_handle_read+0xac5) [0x55ed2d840e85] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(+0x6bd4d) [0x55ed2d716d4d] (on Tor 0.4.5.7 )
Bug:     /lib/x86_64-linux-gnu/libevent-2.1.so.7(+0x2113f) [0x7ffacfbbf13f] (on Tor 0.4.5.7 )
Bug:     /lib/x86_64-linux-gnu/libevent-2.1.so.7(event_base_loop+0x52f) [0x7ffacfbbf87f] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(do_main_loop+0x105) [0x55ed2d718045] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(tor_run_main+0x885) [0x55ed2d7121e5] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(tor_main+0x3e) [0x55ed2d71017e] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(main+0x1d) [0x55ed2d70fd2d] (on Tor 0.4.5.7 )
Bug:     /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf3) [0x7ffacf4680b3] (on Tor 0.4.5.7 )
Bug:     /usr/bin/tor(_start+0x2e) [0x55ed2d70fd8e] (on Tor 0.4.5.7 )

torrc

#BridgeRelay 1
ORPort 9002
ServerTransportPlugin obfs4 exec /usr/bin/obfs4proxy
ServerTransportListenAddr obfs4 0.0.0.0:9003
ExtORPort auto

Possible fixes