Thanks to the work of @oberon, @ant and others, most of the minor kinks plaguing my Manjaro/Deepin install have been ironed out. Even the stuttering on minimise/maximise with Kwin seems to be gone.
There is, however, one persistent issue, and I'm not sure what's causing it, or how to fix it. After several hours of using the computer, my Bluetooth mouse fails to connect (says it's connecting, then says it's not connected) and I need to manually forget it in the settings and it works after restart.
I have my screensaver set to ask password, and this issue (affecting not just the mouse, but also my Google GID6B headset) seems to happen either when waking from screensaver, or waking from sleep. That would point to a LightDM issue? But I think it's happened at other times as well.
I may know a few workarounds that may make this issue more liveable. One way would be to write a service to deal with the suspend problem. The other would be a script to refresh the mouse, triggered by a bash alias or keyboard shortcut.
Obviously neither of those methods fix the issue. It would be best to find the root of the issue. Perhaps disabling tlp temporarily might be a good test to see if its powersaving settings are causing this.
sudo systemctl disable tlp
Reboot, then see if there is any difference with the behavior. If not simply replace "disable" with "enable" in the command, and run that command again to set tlp back in service.
Testing alternate kernels might also be a good idea. Try at least two or three alternate kernels. Install kernels through Manjaro Settings Manager, and always have at least two kernels installed at all times for safety.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 0424:2514 Standard Microsystems Corp. USB 2.0 Hub
Bus 001 Device 003: ID 0a5c:4500 Broadcom Corp. BCM2046B1 USB 2.0 Hub (part of BCM2046 Bluetooth)
Bus 001 Device 004: ID 05ac:0236 Apple, Inc. Internal Keyboard/Trackpad (ANSI)
Bus 001 Device 007: ID 05ac:8218 Apple, Inc. Bluetooth Host Controller
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 002: ID 0424:2514 Standard Microsystems Corp. USB 2.0 Hub
Bus 002 Device 003: ID 05ac:8507 Apple, Inc. Built-in iSight
Bus 002 Device 004: ID 05ac:8242 Apple, Inc. Built-in IR Receiver
-- Logs begin at Mon 2019-04-15 08:34:24 EDT, end at Tue 2019-05-14 10:07:13 EDT. --
May 14 09:54:12 athena kernel: uhci_hcd 0000:00:1a.0: Found HC with no IRQ. Check BIOS/PCI 0000:00:1a.0 setup!
May 14 09:54:12 athena kernel: uhci_hcd 0000:00:1a.0: init 0000:00:1a.0 fail, -19
May 14 09:54:12 athena kernel: uhci_hcd 0000:00:1d.0: Found HC with no IRQ. Check BIOS/PCI 0000:00:1d.0 setup!
May 14 09:54:12 athena kernel: uhci_hcd 0000:00:1d.0: init 0000:00:1d.0 fail, -19
May 14 09:54:12 athena kernel: mce: CPU1: Core temperature above threshold, cpu clock throttled (total events = 1)
May 14 09:54:12 athena kernel: mce: CPU0: Core temperature above threshold, cpu clock throttled (total events = 1)
May 14 09:54:40 athena NetworkManager: <error> [1557842080.3007] sup-iface[0x5599869a4830,wlp3s0]: error adding interface: Timeout was reached
May 14 09:54:48 athena lightdm: gkr-pam: unable to locate daemon control file