Problem with playing all 3 matches again:
If it's a 3-way tie then for those three teams to play again would surely be too much. You could end up with exactly the same situation all over again, i.e. a tie in terms of match wins and not being able to compare points because of a different number of players.

Option for 2v2v2:
I think that a 2v2v2 is an option - potentially the only option if you want a playoff that won't end up with a tie again. It has the potential to be a tie on points but then you just play four more tracks and repeat until it's not a tie any more.

Other options:

Average players points - that way number of players doesn't matter as much.

Average points of top 2 players - because there have been various disconnections and changes part way through matcges etc which may affect an average considered for all players.

Weapons off races (2v2v2) - For me this is the best option if teams are concerned about broken weapons pads etc. It would eliminate the problems with lag and weapons pads and if there is ghosting then it will only make things cleaner and fairer.

Something to consider:
Although it may seem harsh, you could just do it based on points earned. If a team has not been able to put up 4 pilots consistently, then they haven't really taken the advice given when registering their team, in terms of having a squad of 8 with enough backup pilots. If there isn't some down side for teams to only play 3 pilots, then they can always take advantage of that, e.g. by saying they can only play 3 pilots because they know that the other team's fourth pilot is a lot stronger than their own, and therefore they have a better chance with only 3. It a team with 4 or 5 almost top-tier pilots really going to be allowed to come off worse than a team that is actually made up of 2 very top tier pilots and a few filler names who are just there to allow the team to register in the first place. Even if that is considered unfair for this competition, it has to be considered in the future so that teams can't exploit it. Another reason to take this route is that teams who couldn't play a full 4 pilots in group stages due to organisation and availability issues are more likely to cause problems in the following stages. I notice also that the last match in group B seems to be a 2v2. For me this isn't acceptable. In a 2v2, if one players is the very best in the world and wins every race, then the other guy on the team is inconsequential. All he/she has to do is finish each race and that pair wins. This doesn't have much of a team element to it so shouldn't be allowed to be the only thing deciding a particular match, IMO.