First, I wish to thank the creators for this solution.
My HDD also has a hidden partition resulting in the actual partition being recognised as sda2. Parted revealed to me that there is a MSR partition, although I used Acronis Disc Director, no MS tool. ADD doesn't even show the MSR partition it created.
But that shouldn't be an issue, even multiple visible partitions should be mounted correctly, so I took a look at the script and observed that it tried to mount sda1 by the label of sda2, which gave an error, but the already created folder prevented it from mounting sda2 afterwards. Furthermore, it didn't handle labels with blanks correctly because of some path variables without quotes.
So I altered the part that uses ls to retrieve the devices. Now it uses blkid for that, so only partitions with a valid file system are even considered for mounting. I tested it with the internal HDD and some USB sticks, works perfectly for me so far. If anyone is interested, I'm going to attach it, but without any kind of warranty, and hopefully the creators won't be annoyed by me for messing up their work
[attachment deleted by admin]