I still have the same issue,spyserver is not "grabbing" the rtl dongle as it should. I  checked spyserver.config and all seems well enough, tried defaults, tried device as RTL-SDR and numerous sample rates within the accepted perameters for RTL 2k, 1k etc..
Tried with a friends airspy AirspyOne device attached to the unit and default spyserver.config, same results unfortunately.
Any more suggestions much welcomed.
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S912 armlogic has cortex-A53 cores which are 64-bit as is your OS.
You have already installed two fundamental 32-bit libraries (libc6:armhf and libstdc++6:armhf)
Do you also need to install additional 32-bit library for spyserver, I honestly don't know!
I'd check on the easy ones that were statically linked at build time first:
$ ldd spyserver
And if installing any missing 32-bit libraries did not solve the problem, then I'd see if there was any issue with any missing 32-bit dynamically loaded resources (e.g. libairspyhf.so, librtlsdr.so, libairspy.so )
You can use a debug tool like strace to find out which files in what directories the program is trying to access (there will be many misses as it searches through the entire library path, you learn what is important and what is irrelevant by using debug tools often enough).
$ strace -f ./spyserver
(or a quick check for library files only "strace -f ./spyserver 2>&1 | grep -i lib" or files that were attempted to be opened "strace -f ./spyserver 2>&1 | grep open" )
If any required library files were missing, I'd look for the package name that owns the missing library file.
e.g
$ sudo dpkg-query -S librtlsdr.so
And install the 32-bit version, e.g.
sudo apt-get install librtlsdr0:armhf
And then rinse and repeat for anything else that is missing. Oh and never expect any program to have any chance of work correctly when it is being debugging with strace, just run the program directly.
That would be how I would approach your problem.