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Quantum Lock suspends sales due to developers losing access to source code
(store.steampowered.com)
To be fair to the developers, they do elaborate a little further in the comments:
Hey everyone, We appreciate the sudden enthusiasm for our game. When we launched it in 2015 into early access and 2016 into full, we were at the vanguard of asymmetrical games. It was exciting, but it was also our first step down the Dunning Kruger curve. QL has bugs that we cannot fix, shaky net code and overall sloppy design. We left the game up for this long so that players who had friends that wanted to play, could still get a copy. However it has been 9 years with minimal to no activity. So we felt it was right to remove it now.
I don't know enough about this game or it's community to comment much, but the devs don't seem to be bad guys - seems like a story of naive developers making a mistake, but doing their best for their community with what they had. For a niche online game with no DLCs, 9 years is hardly a bad run.