5.1.3 does not fix it for me either. I think they transposed the numbers and really meant 5.3.1, not 5.1.3.
If you look at the end of the KB there are 2 solutions. One stating 5.1.3 and the other 5.3.1.
I don't recall what the last minor build in 5.1.3 is without looking but are you on the last update?
Build 188 is the only 5.1.3 build that shows under the list of patches for ePO 5.1, and that's what I'm running (same as the original poster).
Maybe 5.1.4 will fix it, but that seems to be taking forever to release.
hmm I didnt even know 5.1.4 was a thing.
Why the hesitation to go to 5.3.1? It is an extremely seamless upgrade..
Yes, there are several KB articles going back to late 2015 referencing issues expected to be fixed in ePO 5.1.4
Either way, personally I'm waiting for an even newer release that fixes the SHA1 certificate issue.