Issue with MATLAB datastore

I use the datastore and then readall(datastorename) commands to read ASCII files consisting of vehicle data of various sizes. Each of these files has ~ 1150 ECU labels. I find that for shorter files this works perfectly. For files that are really long (drive duration > 600 seconds), I find that the data gets truncated earlier - eg. for a 900 second file, the data only upto ~650s is present after readall and in a 700 second file, data only upto ~500s. Opening the same files in Excel shows that the data exists correctly upto the end.

I am not sure why this happens and I am not in a position to upload an example of the files (confidentiality issues).

I want to know if this is a known issue with datastore and if there is a better way to do this. I have tried csvread and dlmread and get a memory overflow error for large files. Thanks!