Anybody had such an experience or can recommend extra safety measures?
The golden rule of data recovery is to never modify or work on the original media. Whether that would have mattered in this case, I don't know - it wasn't clear from your post. But it can make or break a recovery.
A two channel recording is typically easy to recover because it consists of a single file that is written sequentially on the file system.
The 4 channel mono recording you describe creates challenges... The data stream is not sequential in a contiguous stream, as you found. That is why the recovery software gave you something that jumps around from file to file.
Recovering the 4 files would mean writing a program that would automate the re-construction. If the material is very important, you might find someone to write a tool. This doesn't sound that complicated. If it was a paying gig, then it is reasonable to pay that person for the recovery.
If you have the option, running your recorder in a mode that results in one multi-channel file would be better. It should greatly ease future recovery....
Why you had this problem is another question. You'll probably want to do some testing. How old is the card, have you used it before, etc?