OS: Windows 10
I use an Ethernet switch to send UDP packets to two other systems (connected directly to that same switch) simultaneously via Python 3.4.4. The same code works on two other dev/testing PC's so I know it's not the Python code, but for some reason it doesn't work on the PC that I want the system to be utilized by. 
When I use Wireshark to view the UDP traffic at 169.254.255.255 (the target IP for sending the UDP packets to), nothing appears. However, sending packets to 169.X.X.1 works. On the other hand, packets sent to 169.X.X.255 are sent, but I receive time-to-live exceeded messages in return. I am restricted to that target IP, so changing the IP is not a solution. I also have it sending on port 6000 (arbitrary), I have tried changing the port number to no avail. Also won't let me send to 169.254.255.1
I have the firewalls turned off.
Thanks for your help.
The strange thing about my problem, was that this exact code worked on the computer in question (and two development computers) previously, but wasn't working at the time that I posted this question.
Wireshark wasn't leading me to my answer (only showing me that the UDP packets were not sent), so I decided to ping the IP via the command prompt. I received one of two errors (destination host unreachable, or request timed out). These errors led me to adding my desired target IP (169.254.255.255) to the ARP cache,  which my problem was solved.
I'd like to thank you for suggesting a possible solution.
Windows/Python UDP Broadcast Blocked No Firewall