Hey @Syn, thanks for reporting!
I’ve encountered this issue as well and @sjka already provided a fix for that (See this comment).
We need to wait for a new openHAB Distro and ESH Build in order to fully leverage the Language Server Protocol support along with the completions (@Kai wink wink 
)
A workaround for now would be to temporarily disable LSP - hit Ctrl/Cmd + , in VSCode and set
"openhab.lspEnabled": false,
"openhab.restCompletions": true
Sorry for inconveniences! 
LSP support is still in a heavy development both in ESH and here, so if you encounter any problems with it, please address them in the github issues.