There are no win10 drivers from Ericsson and Lenovo for the F5521gw. And the most likely they will not be available further.
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So, use win7 drivers in the compatibility mode, there are mentions about success on the forum (probably, win8.1 drivers will work too). Install the drivers from the folder where drivers package will be extracted to launching the following string: setup.exe /wNOAUTOSENSING /wUSELASTKNOWNRADIOSTATE 2, 3. As you understand, Intel MEI and Ricoh drivers are needed.
I know successful cases about ThinkPad laptops based on the SandyBridge (like T420 is) and win10 upgrade, w/o issues, using win10 built-in drivers only, i.e. Not from the Lenovo or components manufacturers. Unfortunately, presently ms update catalog doesn't allow to load the drivers by their IDs, because of error appears. So, I can't explain the cause of drivers issue. Finally, I didn't check out whether Ricoh site has related win10 drivers.