Company without lsp-mode works well.

(use-package company-lsp
  :ensure t)
(push 'company-lsp company-backends)

Adding company-lsp fixed the issue but it is no longer supported. Any fix without using company-lsp?

Seems to happen when I use csharp lsp-mode.
I have (setq company-minimum-prefix-length 2) but it triggers after one character and keep triggering after delete.

What's your lsp-mode version? Can you take io trace when this happens?

@kiennq FYI it reproduces with lsp-start-plain.el

Does it only happen with csharp language server?

@kiennq FYI it reproduces with lsp-start-plain.el

disregard that, I though that I am in another issue.

@kiennq So far I see this problem only in csharp.
I tried again with lsp-start-plain.el and the behaviour is kind of improved. I think this happen when company-yasnippets is enabled.
After I disable yasnippets, the candidates are more relevant but company-minimum-prefix-length is still not working (company triggered after typing 1 character even though company-minimum-prefix-length is 2).

I found out the problem, csharp language server is sending space as trigger character, that's why the automatic completion is triggered even if you type with 1 character (you or Emacs must have insert spaces before the current symbol).
Since space as trigger character is too invasive, I think we can help a new custom setting/defvar to specify the character that will be omitted from the trigger characters list.
@yyoncho WDYT?

Same with https://github.com/merrickluo/lsp-tailwindcss/
Since tailwindcss language server is using space as trigger char as well, it would trigger completion even with 1 space
and with tons of tailwind css classes to complete, the typing becomes extremely slow

Some thing like this might help

(advice-add #'lsp-completion--looking-back-trigger-characterp
            :filter-args
            (lambda (r) (seq-remove (lambda (it) (equal it " ")) r))
            '((name . --filter-spaces)))

I see that happening in both Scala and Haskell and the workaround does not help.

I think I'm hitting the same behaviour with company and lsp:

Despite 'company-minimum-prefix-length' set to '3', completion happens even with 0 characters.