When upgrading my phone (BV8000 pro) with the flash tool, format by mistake, and lost the IMEI, with the SN write tool  I could put it again, but now I only connect to 3g, and lose the signal a long time

What about reflashing it again and performing a factory reset after that?

This had happened to me before, I had just restored a (soft) bricked phone and had lost the imei numbers. I had to find the box to get the numbers and reflashed them using MauiMETA. There was no need for root, just USB debugging and ADB permission. The link to the version I used is below
(Link Updated 19/07/2018)
https://mega.nz/#F!jlBmgSgD!u_uiZ_Dv9KyMQ7sstVRzCg

Thanks for your feedback!

Motionman2008 wrote:

This had happened to me before, I had just restored a (soft) bricked phone and had lost the imei numbers. I had to find the box to get the numbers and reflashed them using MauiMETA. There was no need for root, just USB debugging and ADB permission. The link to the version I used is below

https://mega.nz/#F!jlBmgSgD

Dear Motionman2008, you will have the key of the link,

Goshiro wrote:

Motionman2008
I have the same problem can you give me the key too?
Please?

Sorry about that, I though I'd fixed the link, It should be working without any key now!

Motionman2008 wrote:

Goshiro wrote:

Motionman2008
I have the same problem can you give me the key too?
Please?

Sorry about that, I though I'd fixed the link, It should be working without any key now!

Still not working... do you remember the key? is more easy to share that key... thanks!

sn writer    https://mega.nz/#!EQR0Ua4S!Ai_B1_11OkQEfHsZfVCz6VsbIJuF7VAlJFVDLADwbfo
Off Firmware and other files here  https://mega.nz/#!wGpWmCbD!eUFH3aAvb8yD ... QHbinVsJmU

Here is my experience flashing my BV7000 Pro with the latest firmware (never did it on this phone before).
I flashed my phone with BV7000_PRO_Blackview_20171027 Fix: add the compass menu .
I followed Flash guide v4 but during the upgrade the tool required wipe+download (which as per the guide, that I didn't check thouroughly, means I might loose my IMEIs) and I lost my IMEIs.
Strangely , I first thought that I had issue with SIM2 as the provider in SIM1 did register the card and I even received an SMS. Reading the top menu it showed "Bad IMEI" and this lead me to my journey to recover my IMEIs.

1. I installed an older version of Maui meta 3G v6 and enabled USB debugging
2. I followed a guide to install  USB VCOM DRIVERS and Android_Gadget_CDC_driver
Of course the program didn't detect the phone and windows failed to install the neccessary driver .
3. I installed an ADB driver -> still not OK
4. Reinstalled the MAUI with newer version -> 10.1816.0.01
I took it from a link in forum.hovatek.com . Still no go.
Then I noticed that Windows 7 (I'm using dual boot with linux , but all the guides and tools are for Windows ... ) supports downloading the driver from internet. I clicked change policy and it downloaded a 8 MB driver called "Android" . I have no idea what this driver is, but then the windows properly detected my previously powered-off BV7000 Pro.
5. Next step is to run the program and press the "Connect" button. On the right side you will see several steps.
The tool will point at boot. I connected my phone and pressed once the power button. (in previous versions I didn't have to do that).
Keep in mind that the tool will force the phone in special mode and the phone will stay lit with the logo on - this is expected.
6. Once the phone is connected , you can check that by clicling on the search bar (top right) to select "Get Version". Click on the new window -> "Get version" (or something like that) and if it works - close it.
7. Now comes the real fix. Before going to the "IMEI download" , in the main program press "Load DB" and choose to load from the phone (the other option is to load from a file, but I didn't have such).
8. Once the load is successfull (message at the botom) , search for "IMEI Download" and open that menu.
You have several options. As I didn't remember my IMEIs , I decided to pick random ones.I selected export and saved the file.
Then I edited the file and put 2 identical IMEIs: 123456789101112 . I know... it's not very nice , but still better to have your phone working than not.
Now press import , and the program warns you that the checksum is not correct (once you select the previously exported file) . I agreed that it should correct the checksums and the fileds were populated.
Press "write" to push the IMEIs to the phone and it's successfull. Pressing read gets a success (previously I got an error).
9. Close your IMEI sub-program and press disconnect. The phone turns off and you can power it on and see that it worked.
As a was testing the phone, a friend of mine asked me if I didn't keep my box and luckily it was still there.
10. You can repeat the previous steps but instead of importing from a file , you can type your IMEI in the box and restore your original IMEIs (if you have them of course).

In my case, I have latest ROM, IMEIs back and next time I will read the guides more carefully.

Thanks for reading this long post, but I hope it will help to someone who also hasn't read the guide carefully