For me hidden cells starting from column BM through column AMJ are shown following your procedure. From my perspective definitely a bug to be reported at https://bugs.documentfoundation.org/, if not someone else already reported that issue.
Confirmed:
Version: 7.1.4.2 (x64) / LibreOffice Community
Build ID: a529a4fab45b75fefc5b6226684193eb000654f6
CPU threads: 1; OS: Windows 10.0 Build 19043; UI render: Skia/Raster; VCL: win
Locale: en-US (en_DE); UI: en-US
Calc: threaded
and on Linux as well
Version: 7.1.4.2 / LibreOffice Community
Build ID: a529a4fab45b75fefc5b6226684193eb000654f6
CPU threads: 8; OS: Linux 5.3; UI render: default; VCL: kf5
Locale: en-US (en_US.UTF-8); UI: en-US
Calc: threaded