"Shared" Internal Storage total space not right... - Android Q&A, Help & Troubleshooting

So I have a Asus Zenfone 3 Max 5.5 ZC553KL that has 32GB of storage. I decided to root it, I had to unlock bootloader, install Twrp t o flash SuperSU. Anyway, when flashing SuperSu, something went wrong, or I did something wrong when wiping data/factory reset, because the phone coudln't start the OS anymore, it only boot to fastboot or recovery.
So I ended up having to flash a new ROM. I wiped everything, I had to repair and format some partitions to fix Twrp errors. I flashed the new rom through adb fastboot. Then I found a more*recent Rom, and did it all again.
Right now I have a december 2017 Nougat with Magisk root. But I just noticed when connecting the phone to PC that it shows "Shared Internal Storage" of 6.40GB total space only... I checked on the phone, same thing:
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So I went and installed a diskinfo app:
Why is my Data folder so full? This is a fresh ROM...
I found a Quora thread saying that showing "shared internal storage" instead of Internal Storage is as TWRP bug, and to fix it, a user advised to get stock recovery and wipe data/factory reset, maybe it is related to my issue? ShouldI try to fix it that way?

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Updated
Guys I eventually fixed that. It was a TWRP bug.
Now I have another problem. After flashing roms and updating the phone and root, I noticed that I have IMEI 0 Null and Unknown serial number... But even with a imei null I can make calls and send sms... is that normal? I thought imei null would prevent that. Also there seems to be very hard to fix this issue on this phone since it's not mediatek...