Problems with Keyboard navigation in Articulate 360 file

With the assistance of a colleague, I have created a compliance training that is accessible and uses triggers instead of the player. The player, we found, was creating traps in keyboard navigation, which is very detrimental to accessibility. We have a table of contents and a quiz at the end. What we are finding is that the keyboard tabbing now works fine for the quiz portion of the training, but in the main content, the elements selected by tabbing around work fine the first time through the tab order, but then at some point pop outside the main slide into the address bar and we can't get it to come back without using the mouse to click inside the frame--thus defeating the purpose of keyboard navigation. We've been trying to figure it out, but my colleague, who has a lot more experience at this, can't find any difference between the quiz and the content to explain why this is happening. We created the basic quiz in Quizmaker, imported it into the main presentation, and then added audio and navigation buttons to it since we discovered adding audio and updating the tab order was not an option in Quizmaker by itself (too bad!).

Has anyone else see this happen? Any ideas how to fix it? Help is appreciated, but please explain in layman's terms. I'm new to Articulate and still learning. I need to get this compliance training launched ASAP, so I appreciate any feedback you can give me.