Pre-1920, “Communist” was used to mean communist.
Post-1920, As Lenin and Stalin killed more and more people, communists started to use the term “progressive”, because too many people knew what “communist” was all about.
Post-1940, Too many progressives were too clear that “progressives” and “communists” were the same people. “Liberal” was then invented.
Post 1950, Liberal continued to be used by communists within the Democratic Party who worked on 5th column tactics against the U.S. Constitution. However, the hard-overs went to referring to each other by the euphemism “fellow-travelor”.
Post 1991, the USSR finally fell and with it the clear, daily reminder of the evils of communism. Also by this time, “Liberal” was well understood by the populace and had become a disparaging term. The Left then, probably via the academic neo-communist movement, reattached itself to the old term “progressive” liking the nostalgia of it and thinking that everyone was historically ignorant.
Personally, I like the fact that Progressives self-identify themselves as communists by using the term. Most of them are now not that uncomfortable with straight “communist” either.
They will name themselves about anything to disguise themselves - Fabian, collectivist, populist - I had forgotten fellow-traveler, fifth-columnist, and some others. There’s no end to the new names they will assume when they’ve worn out their welcome under an old name.