You are probably running into io conflicts, wanting to read and write simultaneously to the same file. Note that file access is not instant,
To read:
you need to open the file, read the line at position, close the file
to write
you need to open the file,modify the file probably through an append, close the file
Every read and write it goes through all of the steps that are slower than a tick.
Your write is cutting into your read and vice versa. This is causing problems.
You need to change your way of accessing data.
Write to the csv file and in parallel write to a memory array of strings.
Read from the array and not the file (it will be in memory so no conflict)
If the csv file is only needed to read data in unreal then just focus on in memory access and ditch the file completely.
If reading is over the network then it will introduce even more latency so a file is really a bad idea.
Writing to a file on tick will cause degradation of SSD’s, not a good idea.