Won't open "We encountered a problem with your local email database. Error: An unknown error has occurred (mailsync: null)"

I am using a fresh clean install of mac 10.13.6 on older intel macbook pro. A fresh install from getmailspring.com. When I attempt to open app from applications folder, I get the following message: “We encountered a problem with your local email database. Error: An unknown error has occurred (mailsync: null) Check that no other copies of Mailspring are running and click Rebuild to reset your local cache.”. I have tried clicking rebuild. It’s a fresh macos, so I don’t know of any way there could be other copies installed or mailspring system files that shouldn’t be there. Is this a 10.13.6 compatibility issue? I’m running mailspring just fine on my other macbook pro, also on 10.13.6. But I’ve seen this before on a 3rd macbook pro (also 10.13.6). What can I try? Where can I find alternate install files for mailspring? Thank you!

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