Problem with running a Shiny app after upgrading to R 4.3.1

I wrote an app to create time schedules in Shiny. It worked OK with R 3. Since I upgraded to R 4.3.1 Shiny throws an error:

library(shiny); runApp('hotToR-NR.R')
Error in as.character.POSIXt(as.POSIXlt(x), ...) :
'digits' must be numeric, integer valued

I'm a newbie enough to be absolutely lost, since the 'digits' is not in my code, so it must be somewhere in Shiny.
Can somebody point me in the right direction to solve this?

Thanks in advance.

For better error messages, after you load library shiny but before you runApp use