Google photos keeps asking me to sign in

I am on a macbook Pro, running Yosemite. In the past couple of months I have started having a problem with some Google services getting signed out and requiring me to sign back in and use the Google Authenticator. I first noticed this while using Picassa, which I haven't used in a while but started for a big scanning project. I did some searching around and saw that this was a known issue so I just worked around it.

But in the last week or two, after not using Picasa at all, I am starting to have the same problem with the Google Photos uploader. It seems that this all started with Picasa but I associated it all with the latter.

Now I get a "please sign in" notice and sometimes the sign in fails. But when I do sign in successfully it asks me to choose which folders I want backed up as if it is starting the entire process anew. I've had the uploader indicate it is uploading 150,000 photos! This time it tells me It has 8,600 left.

I've searched around online for solutions but have found nothing that seems to work.

Is anybody familiar with this problem and if so, the solution?

Thanks!