Runtimes for many children's cartoons (with "split episodes") are generally wrong
For example, the shows
https://trakt.tv/shows/regular-show/seasons/1/episodes/1
https://trakt.tv/shows/we-bare-bears/seasons/1/episodes/1
Episode runtimes are listed as 22 minutes & 23 minutes, respectively. In fact, each episode has runtime of about 11 minutes.
The reason for the discrepancy is that these shows usually air two 11-minute stories in a single half-hour (22-minute) block, and the "Watch Now" sources, such as Amazon and iTunes, that Trakt uses for episode runtimes has these episodes grouped together as 22-minute pairs.
But if Trakt lists a single (11-minute) story as one episode, then a 22-minute pair of such stories is not the same thing. The information at the "Watch Now" sources is not information about the thing on the Trakt page. As such, in these cases, the "Watch Now" sources like Amazon and iTunes are inappropriate data sources.
Trakt should recognise that this may occur in some shows and correct for it in some way. Otherwise, current and future shows that work this way will continue to have incorrect runtime information.

Yeah, this unfortunately a side effect for some shows by using the streaming info. Hopefully TMDB and TVDB will support per episode runtimes so we can instead use that info.
I manually fixed these 2 shows to have 11 minute runtimes for all episodes. For now, that will be the fix and we’ll need to manually fix the runtimes when they are incorrect.
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R commented
V3 of TVDB (https://beta.thetvdb.com/) supports individual episode runtimes.