If using Internet Explorer you could try this.
Go to the TOOLS menu and choose "Compatibility View Settings" and then add the MyArchicad website address to the list.
I had similar trouble on a completely unrelated website and this fixed the problem (I was using Internet Exploree 11 out of interest).
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10