I'm using Python 3.8.5 on a 2016 MacBook Pro running macOS Catalina 10.15.3.  This model has a touch bar and macOS communicates with the touch bar via a dedicated "iBridge" network interface.  The iBridge network interface uses a fixed MAC address that is common across all MacBook Pro models (ac:de:48:00:11:22).

Normally uuid.uuid1() picks up my WiFi MAC address (which is obviously unique), but this evening I noticed it was generating UUIDs based on the iBridge MAC address.  Since the iBridge MAC is shared across all MacBook Pro laptops, there's no way to guarantee that the UUIDs are now universally unique.  I'm not sure what triggered uuid.uuid1() to start using my iBridge interface although there was an Internet outage here at some point so maybe the network interfaces got reordered.  The iBridge interface (en5) does appear before my WiFi interface (en0) in the output of ifconfig now.

Here's a quick example of the problem:

greent7@avocado:~$ python3
Python 3.8.5 (default, Jul 21 2020, 10:48:26)
[Clang 11.0.3 (clang-1103.0.32.62)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import uuid
>>> uuid.uuid1()
UUID('32bbad32-de12-11ea-a0ee-acde48001122')

And here's the output from ifconfig:

greent7@avocado:~$ ifconfig
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
	options=1203<RXCSUM,TXCSUM,TXSTATUS,SW_TIMESTAMP>
	inet 127.0.0.1 netmask 0xff000000
	inet6 ::1 prefixlen 128
	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1
	nd6 options=201<PERFORMNUD,DAD>
gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280
stf0: flags=0<> mtu 1280
en5: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	ether ac:de:48:00:11:22
	inet6 fe80::aede:48ff:fe00:1122%en5 prefixlen 64 scopeid 0x4
	nd6 options=201<PERFORMNUD,DAD>
	media: autoselect
	status: active
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	options=400<CHANNEL_IO>
	ether 78:4f:43:5e:b9:86
	inet6 fe80::1c4b:d303:b374:c2f3%en0 prefixlen 64 secured scopeid 0x5
	inet6 fd00:1cab:c0ac:fc82:80e:f701:8302:6287 prefixlen 64 autoconf secured
	inet6 fd00:1cab:c0ac:fc82:1c38:9f17:2073:8eb prefixlen 64 autoconf temporary
	inet 192.168.0.11 netmask 0xffffff00 broadcast 192.168.0.255
	nd6 options=201<PERFORMNUD,DAD>
	media: autoselect
	status: active
en3: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
	options=460<TSO4,TSO6,CHANNEL_IO>
	ether 82:46:1a:46:5c:01
	media: autoselect <full-duplex>
	status: inactive
en1: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
	options=460<TSO4,TSO6,CHANNEL_IO>
	ether 82:46:1a:46:5c:00
	media: autoselect <full-duplex>
	status: inactive
en4: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
	options=460<TSO4,TSO6,CHANNEL_IO>
	ether 82:46:1a:46:5c:05
	media: autoselect <full-duplex>
	status: inactive
en2: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
	options=460<TSO4,TSO6,CHANNEL_IO>
	ether 82:46:1a:46:5c:04
	media: autoselect <full-duplex>
	status: inactive
bridge0: flags=8822<BROADCAST,SMART,SIMPLEX,MULTICAST> mtu 1500
	options=63<RXCSUM,TXCSUM,TSO4,TSO6>
	ether 82:46:1a:46:5c:00
	Configuration:
		id 0:0:0:0:0:0 priority 0 hellotime 0 fwddelay 0
		maxage 0 holdcnt 0 proto stp maxaddr 100 timeout 1200
		root id 0:0:0:0:0:0 priority 0 ifcost 0 port 0
		ipfilter disabled flags 0x2
	member: en1 flags=3<LEARNING,DISCOVER>
	        ifmaxaddr 0 port 7 priority 0 path cost 0
	member: en2 flags=3<LEARNING,DISCOVER>
	        ifmaxaddr 0 port 9 priority 0 path cost 0
	member: en3 flags=3<LEARNING,DISCOVER>
	        ifmaxaddr 0 port 6 priority 0 path cost 0
	member: en4 flags=3<LEARNING,DISCOVER>
	        ifmaxaddr 0 port 8 priority 0 path cost 0
	media: <unknown type>
	status: inactive
p2p0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 2304
	options=400<CHANNEL_IO>
	ether 0a:4f:43:5e:b9:86
	media: autoselect
	status: inactive
awdl0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1484
	options=400<CHANNEL_IO>
	ether f6:38:1e:e0:6c:3f
	inet6 fe80::f438:1eff:fee0:6c3f%awdl0 prefixlen 64 scopeid 0xc
	nd6 options=201<PERFORMNUD,DAD>
	media: autoselect
	status: active
llw0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	options=400<CHANNEL_IO>
	ether f6:38:1e:e0:6c:3f
	inet6 fe80::f438:1eff:fee0:6c3f%llw0 prefixlen 64 scopeid 0xd
	nd6 options=201<PERFORMNUD,DAD>
	media: autoselect
	status: active
utun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1380
	inet6 fe80::afc9:f21a:4d82:2c8d%utun0 prefixlen 64 scopeid 0xe
	nd6 options=201<PERFORMNUD,DAD>
utun1: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 2000
	inet6 fe80::4b52:18b4:5f46:4edf%utun1 prefixlen 64 scopeid 0xf
	nd6 options=201<PERFORMNUD,DAD>