Test results in both directions...
From client to router:
PING 10.2.1.1 (10.2.1.1): 56 data bytes
64 bytes from 10.2.1.1: icmp_seq=0 ttl=64 time=2.912 ms
64 bytes from 10.2.1.1: icmp_seq=1 ttl=64 time=1.765 ms
64 bytes from 10.2.1.1: icmp_seq=2 ttl=64 time=1.170 ms
64 bytes from 10.2.1.1: icmp_seq=3 ttl=64 time=1.768 ms
64 bytes from 10.2.1.1: icmp_seq=4 ttl=64 time=1.736 ms
64 bytes from 10.2.1.1: icmp_seq=5 ttl=64 time=1.850 ms
64 bytes from 10.2.1.1: icmp_seq=6 ttl=64 time=1.007 ms
64 bytes from 10.2.1.1: icmp_seq=7 ttl=64 time=1.811 ms
64 bytes from 10.2.1.1: icmp_seq=8 ttl=64 time=1.182 ms
64 bytes from 10.2.1.1: icmp_seq=9 ttl=64 time=3.040 ms
64 bytes from 10.2.1.1: icmp_seq=10 ttl=64 time=1.897 ms
64 bytes from 10.2.1.1: icmp_seq=11 ttl=64 time=1.807 ms
64 bytes from 10.2.1.1: icmp_seq=12 ttl=64 time=1.036 ms
64 bytes from 10.2.1.1: icmp_seq=13 ttl=64 time=1.169 ms
64 bytes from 10.2.1.1: icmp_seq=14 ttl=64 time=1.736 ms
64 bytes from 10.2.1.1: icmp_seq=15 ttl=64 time=1.696 ms
64 bytes from 10.2.1.1: icmp_seq=16 ttl=64 time=1.832 ms
64 bytes from 10.2.1.1: icmp_seq=17 ttl=64 time=1.772 ms
64 bytes from 10.2.1.1: icmp_seq=18 ttl=64 time=1.260 ms
64 bytes from 10.2.1.1: icmp_seq=19 ttl=64 time=1.569 ms
64 bytes from 10.2.1.1: icmp_seq=20 ttl=64 time=1.775 ms
64 bytes from 10.2.1.1: icmp_seq=21 ttl=64 time=1.852 ms
From router to client:
SEQ HOST SIZE TTL TIME STATUS
20 10.2.1.99 56 64 1ms
21 10.2.1.99 56 64 70ms
22 10.2.1.99 56 64 1ms
23 10.2.1.99 56 64 1ms
24 10.2.1.99 56 64 1ms
25 10.2.1.99 56 64 1ms
26 10.2.1.99 56 64 77ms
27 10.2.1.99 56 64 101ms
28 10.2.1.99 56 64 28ms
29 10.2.1.99 56 64 50ms
30 10.2.1.99 56 64 70ms
31 10.2.1.99 56 64 1ms
32 10.2.1.99 56 64 18ms
33 10.2.1.99 56 64 40ms
34 10.2.1.99 56 64 70ms
35 10.2.1.99 56 64 91ms
36 10.2.1.99 56 64 111ms
37 10.2.1.99 56 64 28ms
38 10.2.1.99 56 64 50ms
39 10.2.1.99 56 64 71ms
sent=40 received=40 packet-loss=0% min-rtt=1ms avg-rtt=51ms max-rtt=111ms
This was done at the same time...
As I already said. Changing client device does not help. This was on 5ghz interface but it is the same on 2,4 as long as interface is on bridge. I tried to add virtual interface which would not be part of bridge and it works then correctly. So, the only problem seems to be the bridge...