As recently predicted, we saw the first annulment of a governor today, when Jubilee Wajir Governor Mohamed Abdi Mohamud had his August 2017 election annulled.
There were several reasons given, the most important of which being that he did not have a degree, and was therefore ineligible even to contest. He declined to testify in his own defence during the hearing. Other grounds mentioned in the verbal judgement were extremely bad administrative procedures due to poor presiding officer training (e.g. submission of photocopies instead of originals, altered forms), plus - it appears - 17 fake polling stations (not yet confirmed if this was genuine or just a paperwork issue) plus the IEBC admitted that its staff had reopened ballot boxes in 12 polling stations after closure and sealing without a court order (for legitimate reasons probably, but a procedural violation nonetheless).
I expect that Mohamud will also be ineligible to stand in a rerun, meaning Jubilee will need to find a new candidate. Jubilee will probably win the rerun, but it isn't a certainty and depends on clan arithmetic and who their nominee will be.