Must turn off Avast Online Security to access my Credit Union

Using a Toshiba 64-bit laptop, running Windows 10 Home, 8gb memory, 1T hard drive.

To be able to log into my Credit Union, I must Disable the Avast Online Security, otherwise I get a message saying the data received cannot be verified and to contact the site owners. I contacted them and they assured me it was not a problem with their site. I believe them because I’ve done business with them since 1972 and have used their online services since they began and have never had a problem.

So does Avast Online Security only work when I don’t use it? Things that make you say, Hmmm.
Would appreciate suggestions so I don’t have to disable it every time I want to go to my credit union site.
Thanks

The problem is not AOS.
Without having avast installed the site has problems also. (see the image)

https://www.ssllabs.com/ssltest/analyze.html?d=www.oneazcu.com
Bad admins there as a fix was released in may for the mentioned CVE vulnerability.