If I was him I'd be shipping it immediately after seeing that. If anything it's encouraging and you should be highly motivated to make your product better knowing that there is competition out there that are actually converting customers. There's very few ideas on the internet that can only sustain one party tackling them. When this guy notices in another 2 years that there's now 3 other people who have launched a similar service while he sat idly by he's going to feel even more silly.
Does your cert have an SCT? It would be strange for a Let's Encrypt cert to be missing it but certainly possible. Try running (replace both example.coms with your domain name)
which should print an SCT extension at the end - my version displays it by numeric identifier "1.3.6.1.4.1.11129.2.4.2" but maybe newer versions display it by name.
Alternatively, I think you might able to go to https://www.ssllabs.com/ssltest/ and see if your cert has "Certificate Transparency: Yes", but I'm not sure exactly what that means.
Anyway, I don't think this is related, the question at hand is about OCSP, which is a different mechanism from Certificate Transparency. (Arguably Certificate Transparency is a replacement for revocation in general being flawed in practice for many reasons, but they're different mechanisms.)
It's a weird coincidence for you but for everybody else it's to be expected as there are dozens or hundreds of people having issues every day.
It's extremely unlikely to have anything to do with this incident.
You should obtain a copy of the certificate which triggers NET:ERR_CERTIFICATE_TRANSPARENCY_REQUIRED and take a look at that. There's an excellent chance there's something else even more obvious wrong (from your point of view as a human) but Chrome decided to focus on the lack of trustworthy SCTs.
My instinct would be that it's likely a middle box (e.g. "anti-virus software" on a PC can install itself to snoop on all HTTPS sites, or a corporate "data loss prevention" proxy or that sort of thing) and the bogus certificate will likely make that pretty obvious if you examine it.
I think it's an interplay between system clock skew, Chromium's SCT validation implementation, and (very) recently issued certificates (which are backdated by 1 hour).
It's a bit of a heisenbug but it's occasionally reported on the Let's Encrypt forums. It always goes away for the reporters just by waiting a little bit.
It would be really nice if a user who runs into this could generate a Chromium event log which would hopefully include the SCT events (chrome://net-internals).
