How bizarre. How can you tell it is them that's doing it? Maybe that provides a clue to how they are doing it.
I have an autovote set up with SteemVoter and a curation trail I'm a part of with SteemAuto. I also have my votes available to a certain threshhold on Smartsteem which can result in certain posters getting a lot of upvotes from me. I think Minnowbooster has a similar feature. I don't know of any other ways a poster can get someone else's upvotes without the personally intentionally giving them.
I will say that it is my fault, I signed up with steemvoter and I didn't bother to go through their FAQ. In their FAQ, they said that they would use my voting power and others who signed up with steemvoter to vote their affiliate account which, @ginabot and @steemsports are part of to run their steemvoter services.
I have solved the problem with them on discord channel.
Thanks for the concern.
@yaanivapeji.
How are you doing today?