Ok. It took some time. And it is a problem after we upgraded certs on my.openhab.org. The old one was expiring today so we switched to letsencrypt.org certs and this was causing the problem. The same happened to myself. As soon as I upgraded java to latest 1.8 version on my opehab’s machine everything started working. So I assume this is an old standing problem - Oracle Java uses it’s own keystore instead of system one and there simply were no CA for letsencrypt.org there 
So I recommend that everybody who experience this problem upgrade to the latest Java version.
Sorry for the inconvenience!
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