A lot of SEO can be undone/is reversible; the kicker is it's easier to go down faster than it is to get it back up. Changing things doesn't automatically (even when done correctly) mean you won't see a drop before a pick up. Google claims to be moving away from "exact" matches in keywords and more toward understanding content (example: degrees and certifications often have to do with acquiring knowledge and learning).
My advice? Page title is one of the most important things Google looks at; make your count. If you are trying to do multiple things with it (location/keywords/NLP), then you have to wait out to see if Google figures it out.
I have seen cases where pages can still rank even without an exact title/content match, but since you've noticed a decline, reconsider consistency across your optimization and content. BTW, as a user, NLP doesn't tell me what NLP is - only the acronym is used and that's not necessarily a good thing. (Ex: GHS? Greenfield High School or globally harmonized system.) How does Google know if your content is relevant to a searcher if it's not clear what NLP stands for?
Also, check the technical and make sure there's no weird coding or broken somethings that could also be in the way. Good luck!