I used monero-wallet-gui to import a paper wallet. Synchronization started from the beginning.
Synchronization ran very fast and perfectly well until the moment when my funds appeared, more or less (between "Blocks remaining: 5500" and "Blocks remaining: 4000).
However, from that moment on, synchronization slowed down very much and, worse, the number of blocks remaining started slowly increasing, not decreasing.
Being a Mac user (OS X Yosemite, 10.10.5), I followed the instructions that I've found here: My blockchain is stuck, how do I "unstuck" it?
More specifically,
a) After rebooting my Mac and before starting the GUI, I deleted the p2pstate.bin file. This did not help: the number of blocks remaining was still increasing.
b) So I stopped the daemon and I added "--block-sync-size 20" as daemon startup flag. I then restarted the daemon. This also did not help: the number of blocks remaining was still increasing.
c) So I checked bitmonerolog and I noticed this message: "cryptonote_core/cryptonote_core.cpp:1123 [1;31mLast scheduled hard fork time shows a daemon update is needed now". In fact, I noticed that my monero.wallet.gui version was 0.10.3.1 while the current version is 0.11.0.0
Question: any ideas on how to solve the problem? Does 5.c above is the problem? I'm downloading the new version of the GUI. Will keep this question updated