Have you had them try in an incognito window? Sometimes that does the trick for me. 

@hummingbirdjames did the idea @Elan gave of having the customer try to access their tasks in GUIDEcx via an incognito browser help solve this?

@hummingbirdjames - Thanks for sharing your experience. Are you using the new “View As and Customer Roles” feature that we have in beta in our Labs option? I wouldn’t expect this to be the culprit, but troubleshooting has to start somewhere :) If you are using the new beta feature, this might be a bug. If not, then it might still be a bug, but related to something else. Either way, I am happy to jump on a call and try to help troubleshoot it. Here is a link where you can schedule time with me: https://calendly.com/ccrossett/product-consultation

With View As now released to general availability, this type of customer user impersonation is the easiest way to validate claims like these.