Reactive/anxious dog – should we go back to basics?

We have a rescue cane corso mix (male, approx 2, currently unneutered). He's honestly near-perfect – no problem in the house, walks beautifully most of the time, fine with new people after some confidence-building, and is the most gentle soul. He was, however, previously abused, has a lot of anxiety in new locations and is dog reactive (this came on in the shelter and is definitely from anxiety/frustration).

We've been working with a trainer on his reactivity and have seen great progress, however recently there have been two incidents that have set all of us back a fair bit:

1. A dog reacted to him first in an area we walk daily, which set home off worse than he has in a very long time. Following that, he was extremely anxious/frantic on his walks for a few days. (I know cortisol can take a while to leave the system)

2. After an amazing session with my mum's dog where ours was on a longline (muzzled) and could look at him, then engage and play with us, he bolted at them as they went to leave and pulled me over in the process. No one was injured, but it was quite an ordeal for all of us.

Since these two incidents he's been improving again – for example, we saw a dog this morning and he had one "pop" and then continued walking, turning back every so often to just look at the dog. This, for him, is excellent.

Our next training session after the second incident is this Sunday, and I'm wondering if we should go back to ultra-basics to work on his anxiety before trying to put him in front of other dogs in a training session again? For example, working on staying in place and waiting, impulse control/prey drive etc. Part of me thinks if we could work on positively tackling the basics that make him feel anxious and build his confidence, it will be "easier" to work on his reactivity again.

For further context, we've had him 5 months and he's a completely different dog to the one we adopted. He was hand shy, terrified of people, and just-about knew "sit". I've no doubt, with patience and confidence-building, we can at least positively manage his reactivity and anxiety.

Thoughts?