I had the same issue with the December update to FlashPlayer. It does not install and the workaround is to install and earlier version and disable security protection. Consequently, unless I really need FlashPlayer, it is always disabled.
Device: Mac Pro early 2009
OS: OS x 10.11.6
Safari: Version 11.0.3
When problem reported in December, Adobe staff thanked me for the bug report but evidently they have either not tried or not succeeded in fixing the bug.
You're only other post to the forums appears to be failed install flash player v 28 in Mac OS on January 13, 2018. Adobe staff asked you for log files, but there isn't a follow-up post providing the files, unless they were provided via private message, and the public post was not updated. Unfortunately, I won't be able to follow-up with the other staff member until next week.