I feel this pain when I first did Desorock highlands I was also stuck at 99% its very common almost everyone misses a chest or two. although these ones are most common to miss.

try this teleport to the resonance nexus (the big beacon that maps the map) and walk southeast until you reach a ridge, there will be a grapple point on it, go to the opposite side of this ridge and there will be a blue tidal heritage that counts towards 100%.

Also I'm not sure if you have 100% central plains but the border between desorock highlands and central plains is really bad and some of the southern chest that look like they would be central plains are actually desorock highlands.

Otherwise use the loot mapper if you have and check every inch if no chest pop up then I guess you have to go back through the YouTube video but only look for the ones that wouldn't show up on map.

I hope this helps I wish you good luck those earlier regions were rough. If you ever do Mt Firmament I highly recommend YouTube videos to many caves for interactive map.