Wow, the Vaporeon isn't dead? (Failed solo)

Most likely lag. If the raid is still on, you can try again.

Not sure about that Gengar, you can blame it on him! ;-)

Every move needs to be "super-effective", in my experience.

Two more Eggys or Venusaur instead of Jolteon and Gengar would have done it.
But I think, your fail is due to lags or GPS drift. In normal gym fights I often have this issue. The Pokemon is obviously dead, but it doesn't faint then.

This exact thing happened to me while I was soloing a Gengar, no health but not fainted. Although, I probably could have had it beat, but someone walked up to me with 30 seconds left in the battle and distracted me enough that I lost a charge move on my 5th guy (which I think was a future sight).

We ended up beating him together in no time, but it would have been my first successful solo.

I did it (Vaporeon has HP) with exactly the same team i used for fighting walls of multiple Blissey in high level old gym system, so it is kind like a nostalgic momen for me
1st time for Vapo raid so i use mons that i am familiar with, and just use most powerfull exeggutor that i have
The timer is at zero, but lucky me the server decided that i win