The problem you mention is the same for all philosophy schools and also for the sciences. Around a core of skilled and experienced practitioners and scholars there is a fringe of half-informed folk with a variety of opinions and conjectures, and from the outside it may be difficult to distinguish the facts and the actual teachings from the cloud of dust surrounding them.
If you go to the heart of Buddhism and Taoism you find complete agreement as to the nature of Reality and its correct metaphysical description. This is a notoriously subtle view for which words that are rigorous will seem paradoxical. When Heraclitus states 'We are and are not' or when when a Buddhist says the self both exists and not-exists they speak rigorously. Thus when one Buddhist or Taoist says the self is real and another says it is not they are not necessarily disagreeing, just focusing on different sides of the equation. This leads a lot of people to assume there is controversy where there is none.
Confirmation bias may become a problem for anyone at any time but the practices of the Perennial tradition make it virtually impossible to fall for it. Theorising is not considered a substitute for establishing the facts and conjecture is discouraged. Anticipating what one is going to discover would be an obstacle to progress since it restricts our mental freedom and channel us into our own self-fulfilling prophecy. Reality would outrun our imagination and concepts and thus confirmation bias becomes impossible.
It is worth noting, however, that these traditions explain God as misinterpreted meditative experience, and this misinterpretation must have a lot to do with confirmation bias and an overly hasty interpretation of experience. So among meditators confirmation bias is a well-understood danger.
As long as Taoism and Middle Way Buddhism endorse the same metaphysical doctrine then the majority of debates can be settled by reference to it. As noted, however, many of those who endorse these doctrines hold heterodox or 'fringe' views, and this can create an effective smokescreen of debate and disagreement that will take same work to penetrate.
In general confirmation bias is not a problem in philosophy since sound logical analysis is not vulnerable to it. The real problem is unsound analysis caused by philosophical bias.