No rows returned from remote MySQL in, working OK locally

Using RMySQL from Shiny (running locally) I have no problem to retrieve data from MySQL database (small table, few rows only). But once the app is deployed ( the query result contains zero rows (but column names are fine!, connection with DB itself seems to be fine, IPs for remote MySQL connection are set, etc.). My table is small (few rows, few columns, so not a problem of some big queries). Looking at the shinyapps log:

Warning in dbFetch(rs, n = n, ...) : error while fetching rows

Tried new R/Rstudio installation, upgrading packages, creating new table (and new database), use both dbFetch and dbGetQuery, limit number of rows (n=-1, n = 10).

I used code exactly like in the last example here: Interestingly, it is working in provided dummy database, but not on mine. My app was working before with no problem, now every table has zero rows. Any idea what might be the reason?