Docker OBFS4-bridge offline after 2-3 days

Hi,
I run an OBFS4bridge via Docker on a Synology NAS. Everything works fine, but the bridge logs off again and again after 2-3 days of operation and gets the offline status. Ports 9001 and 9030 are available and I can’t find anything wrong in the LOG either, it looks like this…

ec 26 13:21:18.000 [notice] While not bootstrapping, fetched this many bytes: 66776278 (server descriptor fetch); 5619 (server descriptor upload); 5671194 (consensus network-status fetch); 753881 (microdescriptor fetch)
Dec 26 13:21:18.000 [notice] Heartbeat: Since last heartbeat message, I have seen 22 unique clients.
Dec 26 19:21:18.000 [notice] Heartbeat: Tor's uptime is 4 days 6:00 hours, with 93 circuits open. I've sent 16.46 GB and received 16.40 GB. I've received 1016 connections on IPv4 and 0 on IPv6. I've made 8156 connections with IPv4 and 0 with IPv6.
Dec 26 19:21:18.000 [notice] While not bootstrapping, fetched this many bytes: 70599749 (server descriptor fetch); 5974 (server descriptor upload); 6060865 (consensus network-status fetch); 809352 (microdescriptor fetch)
Dec 26 19:21:18.000 [notice] Heartbeat: Since last heartbeat message, I have seen 22 unique clients.
Dec 27 01:21:18.000 [notice] Heartbeat: Tor's uptime is 4 days 12:00 hours, with 2 circuits open. I've sent 17.38 GB and received 17.33 GB. I've received 1064 connections on IPv4 and 0 on IPv6. I've made 8779 connections with IPv4 and 0 with IPv6.
Dec 27 01:21:18.000 [notice] While not bootstrapping, fetched this many bytes: 75201368 (server descriptor fetch); 6328 (server descriptor upload); 6493960 (consensus network-status fetch); 839991 (microdescriptor fetch)
Dec 27 01:21:18.000 [notice] Heartbeat: Since last heartbeat message, I have seen 15 unique clients.
Dec 27 01:23:33.000 [notice] No circuits are opened. Relaxed timeout for circuit 3194 (a General-purpose client 1-hop circuit in state doing handshakes with channel state open) to 60000ms. However, it appears the circuit has timed out anyway.
Dec 27 07:21:18.000 [notice] Heartbeat: Tor's uptime is 4 days 18:00 hours, with 15 circuits open. I've sent 17.38 GB and received 17.33 GB. I've received 1064 connections on IPv4 and 0 on IPv6. I've made 8809 connections with IPv4 and 0 with IPv6.
Dec 27 07:21:18.000 [notice] While not bootstrapping, fetched this many bytes: 79536885 (server descriptor fetch); 6690 (server descriptor upload); 6877312 (consensus network-status fetch); 875796 (microdescriptor fetch)
Dec 27 07:21:18.000 [notice] Heartbeat: Since last heartbeat message, I have seen 0 unique clients.
Dec 27 13:21:18.000 [notice] Heartbeat: Tor's uptime is 5 days 0:00 hours, with 15 circuits open. I've sent 17.39 GB and received 17.34 GB. I've received 1065 connections on IPv4 and 0 on IPv6. I've made 8825 connections with IPv4 and 0 with IPv6.
Dec 27 13:21:18.000 [notice] While not bootstrapping, fetched this many bytes: 83342894 (server descriptor fetch); 7042 (server descriptor upload); 7183067 (consensus network-status fetch); 899585 (microdescriptor fetch)
Dec 27 13:21:18.000 [notice] Heartbeat: Since last heartbeat message, I have seen 0 unique clients.
Dec 27 19:21:18.000 [notice] Heartbeat: Tor's uptime is 5 days 6:00 hours, with 15 circuits open. I've sent 17.39 GB and received 17.34 GB. I've received 1065 connections on IPv4 and 0 on IPv6. I've made 8843 connections with IPv4 and 0 with IPv6.
Dec 27 19:21:18.000 [notice] While not bootstrapping, fetched this many bytes: 87579188 (server descriptor fetch); 7393 (server descriptor upload); 7525613 (consensus network-status fetch); 980030 (microdescriptor fetch)
Dec 27 19:21:18.000 [notice] Heartbeat: Since last heartbeat message, I have seen 0 unique clients.
Dec 28 01:21:18.000 [notice] Heartbeat: Tor's uptime is 5 days 12:00 hours, with 14 circuits open. I've sent 17.39 GB and received 17.35 GB. I've received 1082 connections on IPv4 and 0 on IPv6. I've made 8857 connections with IPv4 and 0 with IPv6.
Dec 28 01:21:18.000 [notice] While not bootstrapping, fetched this many bytes: 90622215 (server descriptor fetch); 7755 (server descriptor upload); 7805687 (consensus network-status fetch); 1009717 (microdescriptor fetch)
Dec 28 01:21:18.000 [notice] Heartbeat: Since last heartbeat message, I have seen 0 unique clients.
Dec 28 07:21:18.000 [notice] Heartbeat: Tor's uptime is 5 days 18:00 hours, with 14 circuits open. I've sent 17.39 GB and received 17.35 GB. I've received 1083 connections on IPv4 and 0 on IPv6. I've made 8878 connections with IPv4 and 0 with IPv6.

It looks like Traffic is generated but no unique clients…?!

What is wrong?

Thanks for help