Flew today with the new Go 4 v4.2.4 with no software crashes!  I did the usual tweaks on my hardware, but I'm keeping my fingers crossed.  But, it did perform flawlessly for the first time.  My setup is:

Spark Remote Controller
Motorola Z2 Play phone with 32gb
Android 7.1.1
No OTG cable!

However, the little Google Maps square in the lower left corner of the screen is gone, and something else is there.  Whatever it is, I can't seem to make it function.  It doesn't display any map locations, only a black screen.  What is that?

I tested 4.2.4 android, lost connection on samsung A5(2017) and asus K007 tablet @ 150 mtr , NO OTG!! support.
Back again to 4.1.15 pffff, it seems that the only added the mavic air and not fixed the issues with lost connection and app crashing

Jos A Posted at 2018-1-28 02:00
I tested 4.2.4 android, lost connection on samsung A5(2017) and asus K007 tablet @ 150 mtr , NO OTG!! support.
Back again to 4.1.15 pffff, it seems that the only added the mavic air and not fixed the issues with lost connection and app crashing

I don't use the OTG cable.  I never could get it to work with the version of Go 4 I was using, so I gave up on it.  However, I've had good luck without it, and the problems I was having seemed to be related to something else.  And, I still get the pesky "fly-safe database" notice popping up at startup, but I can't seem to do anything about that.  Just for reference for anyone new, here are the tweaks I'm using with the Motorola Z2 Play phone with Android 7.1.1:

Mods for the phone:
  
Completely eliminate the phone dealing with incoming calls by call-forwarding any incoming calls to another number.

Put the phone in “Airplane Mode” while flying.  This will also turn off WiFi, but you can switch WiFi back on by itself before starting and during Go 4.

If your Android phone supports precision GPS locating, go into that phone setting and turn off location services that use cellular and WiFi for location.  Choose the option to use GPS only for location.

Shut down/disable/uninstall any other software on the phone that may be constantly trying to access network services.  Needless to say, Facebook and Facebook messenger no longer reside on this phone.
  
In general, try not to run any software on the phone that isn’t absolutely necessary while flying.  The idea here is to free up processor time.

If your phone is using an SD memory expansion card, make sure it is a "fast" memory card.  It appears that when I bought my phone, the sales people fudged on my SD expansion card and put in a slower card than the phone specs called for.  That problem has been fixed.
  
Mods for DJI Go 4:
  
Increase the camera buffer from the default 2G if your phone has the memory.  I’ve run mine as big as 8G.  And, clear the buffer before every flight.

People have suggested that you have a formatted SD card in the drone to remedy range and video drop out problems.  However, this didn't seem to help me.

When running in the default 5.8ghz mode, you really need to be line-of-sight with the drone since the shorter wavelength of 5.8 doesn't penetrate obstacles as well as 2.4ghz.  I use a program for Android called “WiFi Analyzer” to see how much WiFi network traffic is in my area before I fly.  This, along with the built-in WiFi detector in Go 4 let’s me find the least congested WiFi channels, and I manually select which channel I want to use in Go 4.  On 01/12/2018, I consistently flew over one mile line-of-sight in clear weather using 2.4 Ghz channel 1 with flawless video stream and no signal drop outs.   And, the key here is “line-of-sight” and a clean WiFi channel.  The more obstacles you have between you and the drone, the shorter your range will be.  And, (if it’s not congested) the 2.4 Ghz band will penetrate trees and foliage better than 5.8 Ghz.  And, don't forget that atmospheric conditions affect WiFi range.  Clear conditions and low humidity work better than high humidity and fog.

Your own flying situation may take some special tweaks, but hopefully these suggestions will give you a good start.

After day two of flawless flying with the Go 4 v4.2.4, it seems to be much more stable on my hardware than the earlier version.  Also, I figured out how to get the small GPS map back in the lower left corner of the "Go Fly" screen.  I used this startup sequence:

1.  Start Go 4 on the phone/tablet
2.  Start the Remote Controller
3.  Start the Spark.

Then, when the Go Fly screen appeared, I had the map back, and I got the message that home had been established.

steve_in_TX Posted at 2018-1-28 17:04
After day two of flawless flying with the Go 4 v4.2.4, it seems to be much more stable on my hardware than the earlier version.  Also, I figured out how to get the small GPS map back in the lower left corner of the "Go Fly" screen.  I used this startup sequence:

1.  Start Go 4 on the phone/tablet

That's good to hear that DJI GO 4 is now working properly with your mobile phone. However, I am also interested in the map issue. Just to verify, what's the interface like when it doesn't show a map in the lower left corner. For mobile phone, the map and attitude indicator will be rolled into one. You can switch the window by clicking the small icon on the right corner on the map. You can refer to the tutorial below. If it is not the attitude indicator, it would be nice if you could provide me with the screenshot for a better confirmation.

DJI Thor Posted at 2018-1-28 19:20
That's good to hear that DJI GO 4 is now working properly with your mobile phone. However, I am also interested in the map issue. Just to verify, what's the interface like when it doesn't show a map in the lower left corner. For mobile phone, the map and attitude indicator will be rolled into one. You can switch the window by clicking the small icon on the right corner on the map. You can refer to the tutorial below. If it is not the attitude indicator, it would be nice if you could provide me with the screenshot for a better confirmation.

When the software didn't show the map, it was just a blank black square in the lower left corner that appeared to have some controls in the corners.  However, since I  got the map back by using the power-up sequence I mentioned above, it hasn't disappeared and functions as it should.

steve_in_TX, thanks for the updates.  I also have the popup to update the fly safe database, but can't do the update.