Ujm,
How do you explain the poskim that rule that they are Jews or the poskim that rule that they are a safek and should only have geirus l’chumra?
1. I don’t know the rationale of those that hold that there is no tzad that they are Jews at all. Every posek I have seen on the issue holds that they are at least a safek.
2. IIRC, those poskim mostly hold that although the Beta Israel believed themselves to be Jewish it is not clear whether (a) the founders of the community were actually Jews (according to one tradition they are descendants of a son of Shlomo HaMelech with the Queen of Sheba and Shlomo slaves) or (b) the conversions they conducted over the years were halachically valid. To put it in context, the DNA studies indicate that 50% of the early female Ashkenazi Jewish population was not Jewish. We presume they did proper conversions k’halacha and so we are all Jewish. But the Beta Israel may not have known the proper requirements for conversion and never properly converted their wives.
3 & 4. This question applies to all Jewish communities everywhere. The Beta Israel have long oral traditions and are referred to in Christian writings throughout these periods. There were numerous wars, edicts and other official Ethiopian Empire acts against the Beta Israel. There’s no reason to thing there was some kind of great switcheroo. I can’t personally ascertain the veracity of any of these writings. But I don’t have any reason to doubt them.