I have a Phantom 4 for a few years now. I've only had about 20 flights and also I use  the Samsung S2 on my controller. My last flight, I had a disconnected message appear on my screen. I thought for sure it was going to be lost. I pressed the RTH button and sure enough it did. Last evening I attempted a flight but could get the copter to link to my Samsung S2. Today I thought I should look into updating software and on my computer I'm using DJI Assistant 2, but the update stops at 98 or 99% and then fails. I've watched videos and tried all sorts of things but now I just feel totally lost.

Hi!
You might be better off posting your question in the 'products' section of this forum.
That is way more active.

My last flight, I had a disconnected message appear on my screen.
I thought for sure it was going to be lost.
I pressed the RTH button and sure enough it did.
Once connection is lost, it's too late to press the RTH button as it cannot communicate with the drone without signal.
But if the drone comes back into signal, pressing RTH will cancel the RTH and leave the drone hovering., waiting for you.

Check your manual to see what it says about Failsafe RTH.
On loss of signal, RTH is initiated and your drone should return automatically.

Hi. I am sorry for the trouble this has caused. With regard to this concern. Kindly please try using a different computer to refresh the firmware of your DJI Phantom 4. In addition upon checking the Samsung S2 is not listed on the recommended mobile device list, this mobile device may work but we cannot guarantee the stability and compatibility during flight, kindly please try a different recommended mobile device to isolate the issue, please refer to the image below for the official DJI recommended mobile device list for the DJI Phantom 4.  Please keep us posted for further assistance. Thank you.

DJI Paladin Posted at 9-15 08:16
Hi. I am sorry for the trouble this has caused. With regard to this concern. Kindly please try using a different computer to refresh the firmware of your DJI Phantom 4. In addition upon checking the Samsung S2 is not listed on the recommended mobile device list, this mobile device may work but we cannot guarantee the stability and compatibility during flight, kindly please try a different recommended mobile device to isolate the issue, please refer to the image below for the official DJI recommended mobile device list for the DJI Phantom 4.  Please keep us posted for further assistance. Thank you.

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So I've just tried to refresh the firmware on another computer. Same result, it goes to 98% and then hangs up then, gives failed message and suggests retry. Which I've done a few times. I use iphone8 so I can park the Samsung S2 but really think I should refresh firmware cause it's never been done to my knowledge.

fans43ea27f1 Posted at 9-17 11:57
So I've just tried to refresh the firmware on another computer. Same result, it goes to 98% and then hangs up then, gives failed message and suggests retry. Which I've done a few times. I use iphone8 so I can park the Samsung S2 but really think I should refresh firmware cause it's never been done to my knowledge.

I am sorry to know that the issue still persists after completing this troubleshooting step. Since the issue persists, there may be something inside the drone that is causing this issue. Kindly please contact our DJI support team to start up a ticket and further diagnose the cause of the issue. Please note that the repair cost will depend on the warranty period of the drone; otherwise, valid charges will apply. Thank you.