I'm guessing this is either a bit of fibrous plant material, or someone built a time machine & left some woven cloth in Burma a long time ago (around 99 mya). The inclusion is roughly 2 mm in length and curved, making it difficult to photograph. Pics 1 - 3 are a top view, 4 is from below & harder to get. Pic 5 is the entire piece of amber measuring 17 mm in length with this inclusion circled in red. So plant material or part of a fairy cloak?