Solved Poor outbound link on vmx after upgrading 12.0 -> 12.1

I have a VPS on CloudAtCost. They have a template for FreeBSD 12.0, and a VPS installed from it works great.
The network performance in average 1.5Gb/s / 800Mb/s (in/out).

After upgrading it to 12.1 the outbound link's speed droped significantly and becomes 0.7Mb/s ― very consistent.
So, definitely something has changed from 12.0 to 12.1.

Thanks for ideas and directions!
Thanks DutchDaemon , good to know!
It looks that in my case disabling TSO helps. Still experimenting.

[EDIT] I corrected previously posted "enabling" to "disabling" ― changed many parameters while experimenting, eventually re-installed the VPS, and the only thing changed now is the added -tso to /etc/rc.conf:
ifconfig_vmx0="inet A.B.C.D netmask -tso"