I’m not sure if this is intended but I can’t find any information on it. It looks like only the first Giant Eye Tentacle and Giant claw tentacles in phase 2 are being counted. Any subsequent Giant Eye/Claw Tentacle that spawn do not look to be counted. The below information I found shares the same conclusion with other guilds and other characters damage not being counted for the majority of Giant Eye/Claw Tentacles in phase 2.
This first picture it says I did 238.1 DPS for the whole fight. Looking into this fight as a whole it says I did 0 damage to Giant Claw Tentacles and only 2.2k damage done on Giant Eye Tentacles. My details addon said I was doing 20k+ combined damage on these adds and I know for a fact that I was targeting them and doing a lot more damage.
These images shows the damage I did to Giant Claw Tentacles and Giant Eye Tentacles during this fight as well as my pet versus what the parse damage shows in the third picture.
This second picture is through the replay feature of warcraftlogs and at the end it has me doing 294.8 DPS. This dps number of 294.8 was the same as what my details damage addon was saying.