When I'm doing bandwith test between two routerboards, sometime happends, that it runs corectly in one direction, but on second direction it shows 0 Mbps. When I'm doing reverse BT (from the second router back to the 1st one), there is same problem but on the second direction.
It is not depended on firewall rules (empty firewall filter on both sides and no firewall in the way.).
Btest server is enabled on both sides.
Not depended on TCP/UDP tests.

In attachement you can see, how it looks like. The test is done from ip 10.100.31.1 (CCR) to ip 10.100.31.2 (RB4011). Same subnet 10.100.31.0/24. No firewall filter. BTest server enabled on both sides.
Btest from 10.100.31.1 to 10.100.31.2 shows 90Mbps receive and 0Mbps send.
Btest from 10.100.31.2 to 10.100.31.1 shows 0 Mbps receive and 90 Mbps send.

It looks like on the screenshot in attachement ...

you can use udp to test it
in some situation ,tcp has some problem .

Are those routers connected with ethernet?
If yes, are ethernets in full-duplex?

you can use udp to test it
in some situation ,tcp has some problem .

udp protocol we have already tried and no difference. Linking routers is via multiple jumps (wireless and cable) using one "vlan". But this problem has already occurred to us even when connecting to wireless. Do you think there will be a problem in "vlan" or do we have to look for a problem somewhere in mikrotik rOS? Thanks