Here is the IEBC explanation. Gadgets with challenges. I am not sure if that is also the explanation for the delayed Form 34As.
Let's agree with that explanation. Still the votes cast on the portal already surpass what was declared. Uhuru officially received 8,203,290; the new numbers on the portal are 8,217,125. Raila's official is 6,762,224; his new numbers on the portal are 6,816,673. The total valid votes declared were 15,114,582. In the tweet the portal is showing 15,168,899. A difference of 54,317 votes.
What's the big deal?
The IEBC claims, in the same tweet that they had received all signed in forms from which the official results were declared. That these results are not new. That means, they have already announced the results for 40,883 polling stations. Yet, the results for 40,842 already surpass the figures they declared. Fewer polling stations, more voters.