Still getting a lot of junk signups–probably bots

I’m getting weird email signups and can’t stop them. I had hoped WPBruiser would help but I’m still getting them.
On my signup form, I have 3 spots to fill in: 1)first name 2)last name optional 3)email. With these weird signups, they fill a first & last name into the first name slot, and again the same first & last name into the last name spot, and then an email that seems to have a completely different name from the first/last name given.
For the most part when they show up, my analytics don’t show a hit on my subscribe button, so it seems like it has to be a bot, right?
I’ve configured WPBruiser to protect my email signup form, and for a few weeks, the weird signups stopped, but now they’re showing up again.
Hoping someone has an idea. (I know I could probably fix the problem with double opt-in, but for reasons I don’t want to go into now, I need to use single opt-in)