I wasn't surprised by the Jessica reveal, but I did find myself a little sad they didn't give Lyatt a couple episodes of happy togetherness before tossing it in the mix. I understand they only have 10 episodes, and that sometimes means slamming on the gas to get thing lined up for the finale, but I think it would have been a stronger story if they'd put just a little more space between "yay, we're in love!" and "oh, poop, dead wife is back!"
It was Lucy, both times.
I do think part of that was to make sure the audience really understood there was hot, romantic lovin' just before it all blows up, but I actually thought it was in-character for Lucy. Huge parts of her life have either been proven to be a lie or have simply been erased. Wyatt has become one of the few constants -- a protector, a supporter, someone who doesn't change even when history changes around them -- so it made sense to me that she'd want reassurance that this next step in their relationship was a real thing that was happening. Right before it all blows up.
She's also the girl who (established just before aforementioned hot, romantic lovin') choose debate club over prom, so it also played as basic insecurity that the bad-boy-turned-soldier had walked away satisfied.
Last week, I would have said they were just trying to flesh out his backstory a little more. Now, I think they're building to something, because...
I think that's your season-finale right there: both Lucy and Wyatt are "purebred" Rittenhouse, and their offspring -- conceived somewhere in the timesteam and technically a fourth person in the Lifeboat -- will turn out to be a necessary part of the Rittenhouse World Domination Plan. I really like Jiya, but I don't think that whole deep-dive into her health had all that much to do with her.
Any guess on what brought Jessica back? I read some speculation that maybe killing the studio security guard towards the end of the episode might have altered the timeline, but my money is on Emma, because, well, Emma is horrible. She told Lucy in 1918 that she'd made repeated hops across time to make sure Lucy's sister could never be born. No reason she couldn't have done the same in Jessica's killer's timeline to make the murder un-happen and fracture the Time Team.