FastTrack and RB751G-2HnD

Hello, there is such a router, the channel is only 100 Mbit/s, but when it is loaded and ~15 kp/s, the CPU load reaches 95%
udp traffic (openvpn client in local network connected to external server) passes through a simple nat, nothing else is configured. I tried to enable fast path and fast track, but for some reason only 1-3kp/s of everything passes through fast track. the ip settings fast track indicator is active, but the number of packets passed through it is very small

/tool profile 
NAME                    CPU        USAGE
wireless                              0%
ethernet                             11%
console                               1%
dns                                   1%
firewall                           25.5%
networking                         24.5%
winbox                                2%
management                            3%
routing                               0%
internet-detect                       0%
profiling                             1%
telnet                                0%
bridging                              1%
unclassified                          2%
total                                72%

configuration: https://gist.github.com/mark99i/59649813a455a2d2cdb2b84ccf214592

can you tell me what I might have forgotten?

Suggestions? anyone