I am curious if anyone can replicate (no pun intended) this issue.
I've been doing some development, and reloading add-ons frequently.
I happened to notice on one such occasion, that I had two NVDA configuration settings entries for Developer toolkit: one near the bottom of the list, and one toward the second third.
For fun, I reloaded add-ons several more times, and what do you know: for each one, another "Developer Toolkit" appeared on the list. I reloaded NVDA entirely and tried again, with the same effect, although it did at least start over at one.
I think I had it up to seven occurrences before the novelty lost its charm.
Latest stable developer toolkit.
Windows 10, 1903, 64bit.
I can provide logs, but there doesn't seem to be anything unusual there.