For a while, since COVID, the Northeast Regional Train #171 did not stop at L'Enfant Plaza, which is an unofficial stop.
Although there were about a dozen people boarding pre-COVID, they seem to have stopped coming, either because they no longer commute or because they think the train will not stop. If it is the latter, the belief is mistaken. For the past month, the train has been stopping, though you need to flag it. Sometimes I am alone on the platform and it feels bad to stop an entire train. So it would be nice to see people return to the stop (and Amtrak should make it official: as an open station, it is a much safer alternative than Union Station).
The northbound 176 also stops routinely and lets a few people off. They do ask me but I think they stop in any case. I would always inform the conductor though.