So far I’ve only noticed this with Hitsugi no Chaika (or Chaika the Coffin Princess), which has a second season called Hitsugi no Chaika: Avenging Battle. Nyaa, Dognzb.cr and Fanzub all fail to find any episodes for the second season, both with automatic and manual search.
The problem seems to be that it’s searching with the absolute number, when all releases I’ve seen start the season from 01.
These are the debug logs from manually searching for the first episode of season 2:
NzbSearchService|Searching 3 indexers for [Chaika the Coffin Princess : 13]
Newznab|Downloading Feed https://api.dognzb.cr/api?t=search&cat=5070&extended=1&apikey=<removed>&offset=0&limit=100&q=Hitsugi no Chaika Avenging Battle+13
Fanzub|Downloading Feed http://fanzub.com/rss/?cat=anime&max=100&q="Hitsugi+no+Chaika+Avenging+Battle 13"|"Hitsugi+no+Chaika+Avenging+Battle - 13"|"Chaika+the+Coffin+Princess+Avenging+Battle 13"|"Chaika+the+Coffin+Princess+Avenging+Battle - 13"|"Chaika+the+Coffin+Princess 13"|"Chaika+the+Coffin+Princess - 13"
Newznab|Downloading Feed https://api.dognzb.cr/api?t=search&cat=5070&extended=1&apikey=<removed>&offset=0&limit=100&q=Chaika the Coffin Princess Avenging Battle+13
Newznab|Downloading Feed https://api.dognzb.cr/api?t=search&cat=5070&extended=1&apikey=<removed>&offset=0&limit=100&q=Chaika the Coffin Princess+13
NzbSearchService|Total of 0 reports were found for [Chaika the Coffin Princess : 13] from 3 indexers
Nyaa somehow manages to find episode 2x06 with the same search term.
NzbSearchService|Searching 1 indexers for [Chaika the Coffin Princess : 13]
Nyaa|Downloading Feed http://www.nyaa.se/?page=rss&cats=1_37&filter=1&offset=1&term=Hitsugi+no+Chaika+Avenging+Battle+13
Nyaa|Downloading Feed http://www.nyaa.se/?page=rss&cats=1_37&filter=1&offset=1&term=Chaika+the+Coffin+Princess+Avenging+Battle+13
Nyaa|Downloading Feed http://www.nyaa.se/?page=rss&cats=1_37&filter=1&offset=1&term=Chaika+the+Coffin+Princess+13
NzbSearchService|Total of 1 reports were found for [Chaika the Coffin Princess : 13] from 1 indexers
DownloadDecisionMaker|Processing 1 reports
Parser|Parsing string '[Commie] Hitsugi no Chaika Avenging Battle - 06 [3C33F139].mkv'
Searching for the season name (Hitsugi no Chaika Avenging Battle) and relative episode number (01) returns the correct results in all indexers when searched manually.
Parsing works correctly though, RSS Sync managed to find episode 2x08 from Nyaa’s recent uploads.