Assertion failed: (map_contains(&worker->tcp_connected, key) == 0), function worker_add_tcp_connected, file daemon/worker.c, line 1997

I am using The Knot DNS Resolver on macOS Mojave (10.14.1). I tested the resolver with 1.1.1.1 and 9.9.9.9 DNS Servers. It works good but periodically (after Mac exits sleep) the daemon stops working and "sudo brew services restart knot-resolver" doesn't help as well. After Mac's reboot it starts working again.

kresd.log tells the following:

Assertion failed: (map_contains(&worker->tcp_connected, key) == 0), function worker_add_tcp_connected, file daemon/worker.c, line 1997.
[priming] cannot resolve '.' NS, next priming query in 10 seconds
[detect_time_skew] cannot resolve '.' NS
[ ta ] active refresh failed for . with rcode: 2
[priming] cannot resolve '.' NS, next priming query in 10 seconds
[priming] cannot resolve '.' NS, next priming query in 10 seconds
[priming] cannot resolve '.' NS, next priming query in 10 seconds
[priming] cannot resolve address 'a.root-servers.net.', type: 1
Assertion failed: (map_contains(&worker->tcp_connected, key) == 0), function worker_add_tcp_connected, file daemon/worker.c, line 1997.
[priming] cannot resolve address 'a.root-servers.net.', type: 1
[ ta ] active refresh failed for . with rcode: 2
[ ta ] active refresh failed for . with rcode: 2
Assertion failed: (map_contains(&worker->tcp_connected, key) == 0), function worker_add_tcp_connected, file daemon/worker.c, line 1997.
[priming] cannot resolve address 'a.root-servers.net.', type: 1
[priming] cannot resolve address 'b.root-servers.net.', type: 1
[priming] cannot resolve address 'g.root-servers.net.', type: 28
[priming] cannot resolve address 'h.root-servers.net.', type: 1
[priming] cannot resolve address 'k.root-servers.net.', type: 1
[ ta ] active refresh failed for . with rcode: 2
Assertion failed: (map_contains(&worker->tcp_connected, key) == 0), function worker_add_tcp_connected, file daemon/worker.c, line 1997.
[priming] cannot resolve address 'a.root-servers.net.', type: 1
[priming] cannot resolve address 'b.root-servers.net.', type: 1
[ ta ] active refresh failed for . with rcode: 2
[priming] cannot resolve address 'g.root-servers.net.', type: 28
[priming] cannot resolve address 'k.root-servers.net.', type: 1
[ ta ] active refresh failed for . with rcode: 2
Assertion failed: (map_contains(&worker->tcp_connected, key) == 0), function worker_add_tcp_connected, file daemon/worker.c, line 1997.
[priming] cannot resolve '.' NS, next priming query in 10 seconds
[detect_time_skew] cannot resolve '.' NS
[ ta ] active refresh failed for . with rcode: 2
[priming] cannot resolve '.' NS, next priming query in 10 seconds
[priming] cannot resolve '.' NS, next priming query in 10 seconds