I noticed strange behavior when converting "text" to "capital lettes"
with expresson "UPPER".
step 1:
e.g: converting "01mai" to "01MAI" (text > to capital letters)
with expression "UPPER"
step 2:
after saving record everything works fine: "01mai" is converted to "01MAI"
>>> please notice that there is a sync going on in the background ...

step 3:
after syncing the app, suddenly "01MAI" is "converted" to "44682"

this only happens with special combinations of "number" + "text":
00mai > 00MAI (correct)
01mai > 44862 (???)
20mai > 44701 (???)
30mai > 44711 (???)
40mai > 40MAI (correct)
please fix this ...
many thanks in advance!
It looks like the values are being parsed as dates rather than text–and maybe only on the server (i.e., not the local app). That would explain why numbers outside the range 1-31 don’t get misinterpreted.
So, confirm that your data source has the pertinent columns formatted explicitly as text–otherwise, the automated default could be number or date. For example, in Google Sheets: