Yeah it happened to me, that's why I hate assist achievements. I had a situation where I did get an assist icon, but it didn't count towards the "collaborator"

So I got 3 assists which was clearly visible when I opened stats with tab button, but at the end of the battle I didn't get a collaborator reward. 

Also I noticed that if I only damage mods I don't get assist at all so maybe that is your case 

Thanks! The issue might indeed be mods related since now all bots have mods, too ( they didn't earlier at my level). 

The possibility occurred to me but I was hoping it's not the case. It indeed makes earning assists unnecessarily difficult.

"but at the end of the battle I didn't get a collaborator reward."

Unless there's a bug, this could be for a couple of reasons:

1. The assists weren't by a single mech.

2. The assists were in different rounds of a match.

I forgot to mention, I did keep that in mind, wrote down assists I had with one mech in 1 round and didn't shoot in 2nd. (Didn't die in the 1st and hid in the 2nd round so I can test this) because I suspected this had happened before, and I was right. It was definitely a bug

Here is an additional observation about the orginal topic. If an enemy mech has mods, and if I fire at the mech, destroy the mods and then continue firing at and damaging the mech, then if somebody else kills it I don't get the assist. But if I start firing at a mech whose mods are already gone and somebody else kills it, then I get the assist. 

It's not 100% consistent but close. It would be nice to get the assist if we had a hand in (aka "assisted in" :-) ) bringing down the mech, mods or no mods.

It took me four rounds last night (3 5v5 and 1 CPC) to get one assist and I was really trying to get assists. I would take my target down to near zero and let a teammate get the kill, no assist registered. It didn't seem to matter how much damage I did or when. If I had tried that in the past, I probably would have had 15+ assists per round. 

I didn't really care much about assists, but not giving proper credit for assists may demotivate players. This happens esspecially in CPC matches, where captures and kills matter the most, and assists never really mattered. Team players (like me) find fun in using support builds and rack assists medals up. Getting no assist medals, even though they helped clear down mod shields and dealt significant damage is a pain most could not understand easily

The main issue is it makes achievements and tasks harder. I don't know about other folks, but if not for those reasons I wouldn't care about them either.

I run into this problem as well. But, it's weird, at times, even though I do not see the assist emoji, I would still get the assist credit at the end of match. Other times, I do not receive any credits for the the assist.