Bitcoin-qt -testnet 0.17.1 Send and Receive buttons do nothing
I believe I should answer this question for the people who may stumble here and would like to know right away what is this issue all about.

If you are building from source and configure your build like:

./configure --with-gui --disable-wallet --SOME-OTHER-OPTIONS

and then you decide you want the wallet and go back to configure and rebuild without --disable-wallet, that is:

./configure --with-gui --SOME-OTHER-OPTIONS

make sure you run make clean before rebuilding.