Here is a short review about SD card.
I had one since the beginning
Samsung Pro 64 Gb Micro SD in my Axon 7, until the update to Oreo, this was actually optimal.
Since the Oreo update, it is indeed possible to integrate the SD card into the internal memory.
Apparently, the performance of my Samsung SD card has not met the minimum requirements to work properly.
I was able to use them, but the capacity was not displayed correctly and although 128 Gb of memory was available I could actually use only 64 Gb.
After a long research, I decided to invest a few € in a new Micro SDXC card.
I've bought a Sandisk Extreme SDXC 128 Gb and no more problems.
The capacity is displayed correctly and the best my Axon 7 has received an unexpectedly noticeable performance boost.
The Sandisk Micro SD card has an A1 label which gives it the necessary performance to boost performance.
Maybe this can help one or the other to eliminate the "Oreo SD card bug".