i've got the exact same issue. i'm curently between 15-25 ping. and since today every time i'm playing my ping is totally unstable.
i am on RJ45 (ethernet) and i've got around 2 ping in ping test, 7 ping in teamspeak but 160 ping in bannerlord.
I've rebooted my internet connexion, as well as my computer and it's the same
I enjoyed playing competitive bannerlord but it's now completely impossible, no feint, no perfect block... this is very annoying.
i'm open to talk about this more deeply on a discord or even teamspeak or whateve as you can see form my point of view.
I'm located near paris and i've got 75ping in NADuel when 160 in EUDuel