kindlegen fails to convert epub

Error(core):E1003: Unknown error in class String.

Error(parsing):E3013: More number of characters are hidden using display:none than allowed limit. Limit: 10000 in file: C:\Users\Codrut\AppData\Local\Temp\mbp_7E2_A_19_F_ 6_5_3A_684_2028_1\OEBPS\toc01.xhtml line: 13

KindlePreviewer 3.27.0, Windows 1809 64-bit

epub opens fine with other readers