Nervous dog + conditioning lowest sim level

Context:

After lots of careful consideration and researching, I got an ecollar and am working with a trainer specializing in sighthound off-leash recall. I’ve got a greyhound mix who’s solid with LLW, basic commands, and we’ve overcome his excitement reactivity. He’s also super timid around new objects and things (bones, toys, shampoo bottles, etc). However, I’d love to provide him full off-leash freedom at safe parks and beaches while still having a way to contact him when he’s far. Hence why we got into ecollars.

I put the collar on him daily for a week or so without even turning it on, then did a conditioning class with my trainer. At first, he only felt the stim at a level 3 or 4 out of 100, and would happily take treats for every stim.

This was going great until I kept practicing after class and accidentally pressed the vibrate button. This spooked him BAD and he completely shut down after that. We ended there for the day and I tried giving him lots of praise and treats. He wouldn’t eat them.

Since then, I tried conditioning the stim again but he still wouldn’t accept treats (even outside of training sessions), just on our walks. The collar is on the entire time too, but I haven’t been stimming on those daily walks yet.

It’s been 6 or 7 days since the incident, and he’s finally snacking on chips with me. He’s still apprehensive about training treats though.

All of this to ask:

He feels the stim indoors on a level 1, and he’d never accept treats during our short training sessions. Should I just wait it out and go a week without stimming but keeping the collar on during the day? How long will it take for him to forget about the vibrate incident? He automatically seeks me out nervously when he’d feel the stim, should I just keep acting like everything is fine in the training and use praise instead?

Note: I have talked to my trainer about this, but since there are so many different outlooks/experiences online, I’m curious what you guys think. I’m curious how others would handle this.