I had seen that drop once in a while, but never see higher than 200 myself. In theory though…
It’s an old post, but data about highest single drop amount of shards is still the same; 6. We now know highest possible total multiplier though. So maximum shards to gain is…
Maximum single drop × maximum chest level × maximum total multiplier =
= 6 × 10 × 4.95 = 297 shards.