Going to try and get a decent log on this (although it doesn't show any errors just the ability spam), but for a Marksman Sniper I would say at least 80-90% of the time when it goes to start combat it just ends up spamming Crouch/Ambush over and over again. What looks like is happening is that it crouches then starts to fire off Ambush, but for some reason it then crouches again cancelling ambush. Normally when it gets in this loop after 3-4 times it will throw one of the grenades and then everything will be fine. Sometimes I have to manually fire a grenade to get it out of the loop.
Once it is fully in the combat loop it doesn't have this problem. If combat starts by something shooting at the bot it won't ever do this. Only if the bot is the one initiating combat.
It seems to be caused when the bot senses that something's in range it will fire off crouch immediately... But the crouch shield is in the wrong position. So it then tries to re-crouch with the shield facing towards the target... but even if it crouches in the right position it still tries to re-crouch.
The only other thing I can think of is that when you crouch you actually move back a tiny fraction. So if that pushes the bot outside of the pull range it is going to move forward and try to re-crouch to get back into range... Even though everything is well in range with the default pull range (so that's why once combat is fully engaged it works fine).
EDIT: Here's a log snippit showing it looping Crouch/Ambush until it cast Frag Grenade.
Code:
[00:30:10.623 D] [POI Set] Type: Kill
[00:30:10.639 N] Killing Vicious Vine Cat with 100% health at 22.78 meters
[00:30:10.829 N] Casting Crouch
[00:30:10.838 D] Completed Cast: Crouch Result: Ok
[00:30:10.918 N] Casting Crouch
[00:30:11.119 N] Casting Ambush
[00:30:11.982 N] Casting Crouch
[00:30:12.851 D] Completed Cast: Crouch Result: Ok
[00:30:12.922 N] Casting Crouch
[00:30:13.027 N] Casting Ambush
[00:30:13.974 N] Casting Crouch
[00:30:14.949 D] Completed Cast: Crouch Result: Ok
[00:30:15.008 N] Casting Crouch
[00:30:15.179 N] Casting Ambush
[00:30:16.043 N] Casting Crouch
[00:30:16.959 D] Completed Cast: Crouch Result: Ok
[00:30:17.016 N] Casting Crouch
[00:30:17.231 N] Casting Ambush
[00:30:18.103 N] Casting Crouch
[00:30:18.970 D] Completed Cast: Crouch Result: Ok
[00:30:19.026 N] Casting Crouch
[00:30:19.230 N] Casting Ambush
[00:30:20.122 N] Casting Crouch
[00:30:20.985 D] Completed Cast: Crouch Result: Ok
[00:30:21.043 N] Casting Crouch
[00:30:21.494 N] Casting Fragmentation Grenade
[00:30:22.136 N] Casting Crouch
[00:30:23.005 D] Completed Cast: Crouch Result: Ok
[00:30:23.064 N] Casting Crouch
[00:30:23.263 N] Casting Ambush
[00:30:26.184 N] Casting Explosive Probe
[00:30:27.701 N] Casting Rifle Shot
[00:30:28.229 V] [Poi.Clear] Reason: Targeted unit is dead, clearing Poi and carrying on!
Also, by it re-crouching like this it negates the Ballistic Dampers passive skill you get in the Marksmanship tree (which really sucks in a bad situation).