The gem description is missing the following lines:
quality: Supported Triggered Spells deal xx% increased Damage
mod: Supported Triggered Spells deal yy% more Damage
Note that the datamined page from poedb is also missing these lines.
https://poedb.tw/us/gem.php?n=Cast+while+Channelling+Support
However, a search using the trade website shows the missing lines:
https://www.pathofexile.com/trade/search/Standard/G69e49hb