Jim, to answer your question, I don't think this is a case where the extensions actually interfere with each other.
In general, it is as Linda said, the extensions are tools that allow things to be done quickly. If they are used incorrectly they therefore allow mistakes to be created quickly. In this case 4 powerful/advanced extension features were used (Add Person Redesign, Save Person Data/Set fields from..., Build all Citations, AutoBio).
I think in this particular case there may have been a messaging problem (maybe via word of mouth) when the WikiTree BEE "Get All Citations" was replaced with the Sourcer "Build All Citations". If a WikiTreer had developed a flow using Add Person Redesign, Save Person Data/Set fields from..., Get All Citations, AutoBio that was working fine and they heard that the BEE Get All Citations had been replaced with Sourcer Build All Citations and they didn't check out the options for Build All Citations but just kept using the flow without checking the results then then this is what would have happened.
Build All Citations is a superset of Get All Citations and it can be used pretty much as a straight replacement but only if the option "Add/Merge -> FamilySearch Build All Citations -> Type of citations to generate" is changed from the default of "Narrative plus Sourcer style inline citation" to either "Sourcer style source citation" or "Source citation using text on FS Sources page".
Edit: actually, I think the BEE Get All Citations also had an option to generate inline citations but that may not have been the default.