Wed Aug 5 2020 20:41:14 UTC
It's not a bug, it's a feature.
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ID Product Comp Assignee Status Resolution Summary Changed
58005 POI SXSSF dev RESO DUPL Amount of CellStyles is still limited to 32K 2015-08-19
53209 POI XSSF dev RESO DUPL Too many styles corrupts the excel 2015-09-03
2 bugs found.

as

File a new bug in the "POI" product