I entered this test PLC code, it seems to me working fine:
START
print1 "This aip1 =" aip1
print2 "this is string =" str1
delay 1000
end
First, PLC program all lines converted to upper case, including the string literals. Then space at end of string literals are stripped off.
I stored TRING1 in the str1 entry for the string table, which can be upper or lower case, that caused line2 longer than 16 characters, so that line 2 automatically started scrolling its contents from right to left, that is feature of UM216 LCD module.