I am sorry to hear that you have encountered unexpected behavior while trying to access coursework. That is frustrating!
A 403 error means in general that the request to load content in Buzz was received but was prevented from performing the action. There can be multiple causes for this reported behavior that would require more in-depth analysis. One example is if the activities are using LTI and there is a cookie issue with loading the contents of it. The workaround in that example is to change the activity settings in Buzz to launch the activity in a new window.
I recommend that you report this behavior to your online education institution and if needed, they may escalate it through their regular support representative channels to Agilix Support.