I would not be too concerned.
I think its more an annoying technical glitch than anything more sinister, the site is encrypted and even I cant see users passwords due to the encryption. My rudimentary understanding is there is a digital certificate/key which basically allows the handshake to occur. These handshakes need to occur to allow encryption. The issue can be at the user end or at this end.
I belive that the encryption is good (it passes all tests), however a bit over sensitive. When I used an old PC (with time and date totally wrong). I came up with a similar issue. Dane from TIA experienced a similar issue when using wifi (probably insecure connection) in Azerbaijan. It was resolved when he changed wifi.
From old browsers to expired certificates there are various potential causes.
Did it resolve itself, or are you still having a problem?
I hope its not an issue on this end (I have just done a test and everything seems to be good). However, equally it could be my fault from when I attempt to move server then reverted back a few weeks back.