Here’s a copy of my post in the Arch Forum here: https://bbs.archlinux.org/viewtopic.php?id=229833
Running Arch XFCE LTS kernel, also tested on Arch Cinnamon LTS, and Manjaro Cinnamon LTS (same results)…
Just updated android-tools from the 7.1.2_r27-1 to 8.0_r4-2. Phone connects to pc as usual, but as soon as you try to enable MTP, the phone disconnects immediately and continues to bounce between being connected/unconnected until you reboot the pc (nothing wrong phone side other than the usb connection status/usb debugging going on and off in the status bar). Result differs device to device. On my Moto X Pure I could not connect to ADB at all. Even in charge only mode, as soon as an ADB command is given the device disconnects, along with no MTP access at all. On my LG-G3, ADB works while the phone’s USB setting is in charge only mode, but not in MTP mode - device disconnects. The LG can maintain an MTP connection, but no storage locations are shown (blank in the file manager).
Downgrading back to 7.1.2_r27-1 fixes the issue - ADB/MTP work as they should. Android-udev is unaffected, the latest update works on both versions of android-tools. So for now I’m operational, just wanted the issue noted here.