This is just a report and you can close this issue immediately.

I used to get strange horizontal stripe patterns in plot_hexbin_meta when I used the old schex.

I believe this is probably not a schex or hexbin bug, but a ggplot2 bug reported at
tidyverse/ggplot2#5165

I've not been able to check the details of the code, but I am sure because I could reproduce a similar pattern by using ggplot2::geom_hex.

This bug seems to be solved by updating the version of ggplot2 to 3.4.1 or higher.

In fact, the version of ggplot2 in my environment was 3.4.0, but installing the latest version solved the problem.