Opera version is 54.0.2952.41 from official Opera repository (I switched to it from LEAP version when was unable to sign in). The issue: when I go `Syncronyse->Sign in` I see the loading spinner that is spinning endlessly and nothing happens. In previous versions after clicking "Sign in" the authentication dialogue popped, but after providing my credentials the message appeared telling me that the user or password is wrong. Login and pass were totally fine because I have another computer with LEAP 15 and I'm able to sign in there. There is a difference in installations between two machines: the one that has malfunction Opera is a clean installation and the one with working was updated from LEAP 42.3.

There is a number of threads like this one at official Opera forum describing similar problem. Unfortunately at every one of them developers have no clue or don't want to admit that the issue exists and usually users reports that the issue is gone after updating to one of the newer Opera versions (no help or clue for the
root of the issue from the developers). I've updated Opera several times during last 3 weeks and the issue persists.

If I start Opera from console I see following messages (don't know if it is related to the described issue):
[11159:11159:0701/111914.459310:ERROR:buffer_manager.cc(461)] [.DisplayCompositor-0x23abbedb2a00]GL ERROR :GL_INVALID_OPERATION : glBufferData: <- error from 
previous GL command
[11131:11389:0701/111944.748857:ERROR:cert_verify_proc_nss.cc(980)] CERT_PKIXVerifyCert for auth.opera.com failed err=-8181