Hello alchuikov,

Have you tried accessing your account via private browser and making the client inactive?

Just press CTRL+SHIFT+N and then log in to QuickBooks. Then, try deleting the client again.

If you're able to make it inactive, you can go back to your main browser and clear your browser's cache.

Also, using a different browser can be an option, too.

If you're experiencing the same, please contact our Customer Care Support so we can investigate further.

Get back to me if you have further concerns. I'll be here to help.