I have an existing Mikrotik wireless link for internet distribution and VPN. The system was running well. But, when I upgraded the old MT Version (2.9.26) to new MT version (2.9.41), our wireless link was unstable. Finally, I found the problem is coming from COMPRESSION at interface WLAN—> Advance —>Pramble Mode —> Compression. When I tried to leave the compression box unchecked (leave it blank), no problem arise. Is this one of the problem of the version 2.9.41 or something else?
if its any help, i can confirm that a p2p SR9 link i have using “compression”, both sides just survived an upgrade from 2.9.27 to 2.9.40.
so 2.9.40 is ok with compression.
Yes, you right. The version 2.9.40 is ok with compression. We have so many wireless link with various version and this week will be upgrade all 
I have had to turn off compression on a few links because some how the routing gets messed up. Every thing looks ok but IP pings don’t work, but Mac pings do. So I Mac telnet in only to see watch dog reboot it. It comes up but still not IP traffic. So I MAC telnet again and turn off compression and the IP ping start working again and traffic passes once again.
The Covington units this happened to are running 2.9.41 CPE to a 2.9.40 AP, both rb532s.
The New Orleans units this happened to are running 2.9.29 CPE rb532 to a VIA 533 mhz 2.9.38 AP.