Just out of interest, are you running on a virtual machine, by any chance?
I noticed that on the same macbook pro laptop, I am running the same copy of Windows 10, and the same version of Pokefarmer, but one is as a virual machine, and one is native in boot camp. When it runs native, I don't get this "failed. Trying again" pokestop errors, but when it runs in a virtual machine I do, (even though both are running the same Pokefarmer version (1.89), on the same copy of Windows, on the same hardware)...