Hi RipNoCellular,
Your problems sound just like mine. If so, then your WiFi is still working, but your 2018 MBP looses its DNS information which disconnects you from the Internet and also potentially from your other LAN machines. The DNS problems can be verified by running the following Terminal command:
>
date; ping www.apple.com; date
When the DNS is not working, this command returns an error stating that:
"
ping: cannot resolve www.apple.com: Unknown host"
If DNS information is available, then you will see the received packets:
"
PING e6858.dsce9.akamaiedge.net (104.112.255.7): 56 data bytes
64 bytes from 104.112.255.7: icmp_seq=0 ttl=47 time=71.718 ms
64 bytes from 104.112.255.7: icmp_seq=1 ttl=47 time=68.654 ms
64 bytes from 104.112.255.7: icmp_seq=2 ttl=47 time=63.294 ms"
and you will need to ^C (control-C) the ping command.
I find that these WiFi connection issues are rare (a few times a day), random (they occur while running any utility or app), and often intermittent (they often fix themselves in 1 to 10 minutes, but I've also had them last for 16 hours). These WiFi disconnects cause numerous other problems for me. For instance, Software Updates have failed, Mac App Store updates have failed, Time Machine backups to a Time Capsule have failed a number of times, AirDrop failures, ping failures, rsync failures, ssh failures, Safari failures to load web pages, etc.
I also experience rare, random, and intermittent bluetooth disconnects, especially with my Magic Keyboard and Magic Trackpad. Now bluetooth is still working, and often only one or the other will loose connection (and the battery levels are 90+% when I get a disconnect) with the remaining one still connected.
On a scarier note, I have even seen the macOS (on a clean reinstall with no other software loaded) inappropriately delete a file from an SMB-mounted HDD, once again probably caused by a WiFi disconnect in the middle of modifying the file.
I have carefully documented all of these problems and uploaded the documentation to Apple, but to no avail. Since the machine (my third 2018 MBP) passes hardware tests, Apple says there is nothing wrong with it.
I have found no fix for these WiFi/bluetooth problems (except manually power cycling the WiFi/bluetooth), and I believe we just have to live with them if you wish to continue using your 2018 MBP.
Good luck,
Solouki
EDIT: And yes, I just experienced another WiFi disconnect under 10.14.4.
EDIT 2: I have also experienced WiFi disconnects under 10.14.5 too.