When you say "backups", do you mean special folders created for that reason, or just folders you created and added whatever files you wanted?
Explorer must be encountering something that causes it problems. Perhaps due to that specific drive and/or some proprietary software installed on the drive, or even some type of corruption.
What you are seeing is not normal for an external drive, so perhaps the drive's software may need to be updated. What type of partitions do you have on the drive. Any chance you could get a snipping tool picture of your Disk Management windows and attach using the Upload File option?