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Consider ignoring LSP/tsserver diagnostics unless explicitly asked for #1172
For LSP especially, diagnostics could be sent to the client at any time, even when the client hasn't asked for them. It might be an idea to set a flag when ALE asks for files to be checked, and reset the flag the next time diagnostics appear, so ALE only updates the problems for a buffer when ALE has asked for diagnostics.
Either this will probably need to be done, or the documentation will need to be updated stating that problems could be updated for LSP linters at any time. The latter might be preferable.