Here I discuss a major issue with the latest SteamVR Hotfix update, which can disable use of Pimax headsets.
Here you can find the details of the update:
SteamVR Hotfix
As reads from the page,
Replaced “safe mode” with finer grained control over individual add-ons. After a crash, users will still see some add-ons are “blocked”, but they can be unblocked individually to determine which ones are causing incompatibility.
This is very bad for Pimax headset users, because as many of you know, restarting Pimax services would force quit SteamVR and put it in Safe Mode – but now, the only way to turn off the new Safe Mode is by re-enabling every “add-on,” including the Pimax driver. The big problem is that you can’t access settings in SteamVR without the headset connected to SteamVR; without the Pimax add-on enabled, your headset can’t connect to SteamVR to fix it in the first place. The scenario is similar to Windows Update telling you it can’t update the computer without a Windows update.
I’d just like to to point this out for anyone having the issue. In the meantime I recommend that everyone stay on the version before this if they can.
If already updated, I have found a temporary solution for this issue, but it’s a bit of a hassle to do this every time and I can’t guarantee it will work forever.
It’s the same solution people use to use SteamVR without a HMD. Here’s a link to that:
Use SteamVR Tracked Devices Without a HMD
From the page linked above:
" First Just add “activateMultipleDrivers” : true, “forcedDriver”: “null”, to near the top of the “steamvr” section of your steamvr.vrsettings config file.
{
"steamvr" : {
"activateMultipleDrivers" : true,
"forcedDriver": "null",
"allowAsyncReprojection" : false,
"allowInterleavedReprojection" : false,
"allowSupersampleFiltering" : false,
"enableHomeApp" : false,
"mirrorViewGeometry" : "1387 675 2272 1270",
"showMirrorView" : true
}
}
C:\Program Files (x86)\Steam\config\steamvr.vrsettings
Secondly Set enable to true in null driver to enable it.
{
"driver_null" : {
"enable" : true,
"serialNumber" : "Null Serial Number",
"modelNumber" : "Null Model Number",
"windowX" : 0,
"windowY" : 0,
"windowWidth" : 1920,
"windowHeight" : 1080,
"renderWidth" : 1920,
"renderHeight" : 1060,
"secondsFromVsyncToPhotons" : 0.01111111,
"displayFrequency" : 60.0
}
}
C:\Program Files (x86)\Steam\steamapps\common\SteamVR\drivers\null\resources\settings\default.vrsettings "
Don’t close the default.vrsettings page.
After setting and saving these, open SteamVR. Go to your settings, which should now work. Enable your add-ons again, more importantly the Pimax add-on.
Quit SteamVR.
Go back to the default.vrsettings document. Change “true” back to “false” and save.
Make sure PiTool is running, then reopen SteamVR. Everything should work again.
Credit goes to balderik and bendotcom
After you did step one the first time, you only need to change default.vrsettings from “true” to “false” and vice versa; there is no need to remove the text from the first step.
UPDATE:
@dillanski has found a better solution:
I recommend making steamvr.vrsettings a read-only file to prevent this from happening in later versions
Nice find! 
