Router blocking HTTPS ?

Hi

Bought a GETNET GA524WA Modem/router as a stop gap when my speedtouch died.

All set up and working well , good connection speeds etc.
Only problem is I cannot connect to secure sites i.e HTTPS.
Everything else no problems.

Connected the laptop, same problem, cannot connect using a Tablet either.
All of which suggests that somehow the router is blocking secure sites ?
Routers firewall is set to allow all traffic.
Anyone any Ideas, tried the manufacturer bur seem to have hit a brick wall there.
Re flashed the firmware of which there is only one version.

Tried changing the NTU 1400 1420 1440 1460 1480 1500 no difference.

Any help much appreciated.

Keith