Split episode second part missing

I have the series The Office (US) which regularly has split episodes. According to the thetvdb website each part has its own episode number, which is how I've named my files (I am using the default scraper for thetvdb). For instance:
The.Office S05E14 - Lecture Circuit Part 1[720p].mkv
The.Office S05E15 - Lecture Circuit Part 2 [720p].mkv
The.Office S06E04 - Niagara Part 1 [720p].mkv
The.Office S06E05 - Niagara Part 2 [720p].mkv

Each episode is in its correct episode folder and the episode folders is in the correct TV series folder. The scraper seemingly works without a problem. In Kodi though for the sixth season split episode the second file is ignored. The fifth season split episode doesn't have this problem: episode 14 and 15 are displayed in that order with that episode number in Kodi. For season six however the files are renumbered. The 6th episode becomes the 5th, the 7th becomes the 6th, etc. The second part of the split episode is left from the Kodi episode list completely and the season numbering is changed from the original numbering that is on the thetvdb website. The split episode is still in two files though, so the second part is gone from the kodi list.

tl;dr:
my files have split episodes as two files
thetvdb has the two parts of a split episode as two separately numbered episodes.
for season six kodi only displays the first part of a split episode, and numbers the season differently as thetvdb where it's supposed to scrape from

How can I get kodi to match the season numbering from thetvdb?