Hey Hive account@htooms
I think it has nothing to do with slow internet connection.
It happens due to the time lag between the creation of new blocks, as we know that it takes minimum 3 seconds to generate a new block.
Every new block accommodates the new information on the steem blockchain whenever we upvote flag post or comment the new information has to be fed into the blockchain.
Sometimes when people use the platform simultaneously the block gets filled and new transaction (in this case upvote) has to wait until the next block is generated which takes 3 more seconds this continues to happen until it finds an empty block to fit in.
We generally do not observe this since block generation time is too small (3 seconds)
This can happen not only in case of upvote slider but also in case of posting and resteeming.
Different browsers show this in different ways
In your case it showed a rotating arrow
In my browser it shows a rotating ring.
Hope you found this useful.