I'm running LibreELEC on a NUC7PJYH. The built in Realtek RTS5229 PCI Express Card Reader worked fine with LibreELEC 9.0.2.
After updating to LibreELEC 9.1.002 or 9.1.501 the card reader isn't detected anymore. I've also tried the latest Milhouse Testbuild and Weekly Linux 5.3-rc8 build #0909x with the same result.
It seems the problem started with Linux Kernel 5.0.x. There is a bug report on Bugzilla RTS5229 built in card reader not detected after Linux 5.0.x, but no real progress.
Is there any chance to get the card reader working again with the latest LibreELEC versions?