The Chimera MBT doesn't have icons in Recursion Online, so when you get kills in it it shows as a "Missing Image".

Additionally, killing ESFs with the main gun does not award the Fly Swatter achievement.
Here, I killed two Mosquitos with the CT-150 Cyclops (timestamps 01:21:11 and 01:31:06) and was not awarded Fly Swatter.

The Dervish also doesn't have icons, nor does the Chimera's newest main gun "Larion PPC"
I also notice that the Prowler's "P4-120 Kingsnake" lacks icons