Like other LSP servers (see Classic confinement request for ccls and Classic confinement for gopls for other similar requests in the past for other similar snaps) bash-language-server expects to be able to access executables and other files from the host system (e.g. https://github.com/bash-lsp/bash-language-server/blob/633e206eec662621497a98aa4e52e2b586992681/server/src/executables.ts#L51).
As such it is not able to function correctly under strict confinement.
As a LSP server implementation, it fits within the existing category of compilers/debug tools etc as per Process for reviewing classic confinement snaps.
Thanks