Another instance of this are DNS - which is pretty much always called domain name server server (DNS server)
Though you can at least have an argument there, as the first server could theoretically be the process that's running on the hardware/virtual server (which would be the second server).
even the original rfcs from 198x only write about domain name servers though, which is why the DNS server is still a misnomer of the same kind, even if my attempt of rationalizing it failed - as that's the only thing you've called into question with that.
Because if domain name system server makes sense to you, then language server protocol server has to make sense in the same way, as that's literally the same concept
LSP Server does make sense, the problem is that the title calls it a "HTML LSP", not a "HTML LSP Server". The thing described is a server, not a protocol.
Though you can at least have an argument there, as the first server could theoretically be the process that's running on the hardware/virtual server (which would be the second server).