No problem Johschr, glad to help.
You could see what is stored in MI900 and following registers by opening block "SD Utility Delimited Line". There you will see data that is written. It will be couple of rows of what is to be written into CSV file, each row in this block will be data in consecutive columns.
Ex.
#1 Indirect text - ML 15 (Because you have a function block that turns date into ascii in line 1 of your code)
#2 Indirect text - ML 10 (Because you have a function block that turns time into ascii in line 1 of your code)
#2 Numeric field - MI0 (Maybe a process value, pressure)
So block "SD Utility Delimited Line" will take all those fields, add delimiters on the end and store all that into one line of ascii characters starting from MI900. That's how to see what is in MI900, basically one row of your CSV file.
It could be that MI900 quickly changes value when function is called because it first holds titles of columns until they are written in line, and then gets overwritten with process data.
Can't really say what is causing PLC to freeze. Looks like up arrow on keyboard is used to reset status bits from one write function to allow the next one to be called, from what I can see in the pictures. Does data get written into CSV after pressing it? Maybe there is some sort of conflict if you are accessing and SD card while PLC is writing to it. Just guessing now, troubleshooting someone else's work can be difficult.