Sure:
General Settings -> General:
- Domain: http://domain.tld/
- WHMCS System URL: http://domain.tld/
- WHMCS SSL System URL: https://domain.tld/
General Settings -> Security:
- Admin Force SSL Access: True
- Disable Session IP Check: True
And now you have to click from Admin Area to Client Area, login with an Account in the Client Area, change back to Admin Area, login to another user via Admin Area, go to Client Area log off, change back to Admin Area, change to Client Area, get back to Admin Area, login in with an User through Admin Area, go back to Admin Area, login in as another User, log off, Close Browser, Open Browser, order something, get back to Admin Area etc.....
In Short: "You have to use WHMCS to get this Problem".
Often you get this Problem after a few Days, i login via aWHMCS, via Opera Browser on Smartphone, with my Laptop and with my PC - i also have many devices who is use WHMCS with.
I can not say exactly how you can reproduce this.