Q: Time Machine Back Up creating multiple folders

The only thing you are doing wrong is looking at the contents of Backups.backupd.

That directory is the domain of Time Machine: what you are seeing is completely normal. Essentially each new folder only contains the changes that occurred since the previous update. If there are no changes, or only af few, the backup will complete very fast.

A nice overview of how it works can be found here: http://pondini.org/TM/Works.html

OK, first of all check if the exclusions list is empty: http://pondini.org/TM/10.html

Then there is a (hidden) list of exclusions that Time Machine uses, containing all kinds of temporary fluff, like caches. Usually these aren't very big though. And lastly some virtualization software, such as Parallels, has an option to ignore the 'virtual machine' in TM backups.

If none of this applies, please say so.

What does 'Storage' show? (Apple symbol in menu bar -> About this Mac>

Yup. Anything odd about the distribution of that used storage? Or does it look about right?

That's not what I meant... Do the numbers of the different sections make sense? Or do some seem extraordinary high to you? E.g. If you hardly have any music, a number of 60 GB would be odd.

To get a more precise idea of what is on your Mac, you also can use Omni Disk Sweeper: https://www.omnigroup.com/more/

What I'm trying to figure out here, is if the remaining 70 GB consists of useful files or not. Sometimes the sizes of cache files, swap files and 'sleep image' get out of hand, and TM will ignore these. For more information see http://pondini.org/OSX/DiskSpace.html

If my previous reply still doesn't brings a solution, you can check the following pages on the Pondini site:

http://pondini.org/TM/8.html

http://pondini.org/TM/9.html

http://pondini.org/TM/10.html

http://pondini.org/TM/D10.html

http://pondini.org/TM/D10a.html