I have had the same issue. When my rabbit goes into stasis we cant feed her critical care because of the gas and had to get grain free pellets to soak which caused less gas.
Maybe your rabbit has a slight intolerance to grain?
Her gas was so severe it lasted months. We had better success with grinding down her hay fine but not a powder. This is digested more slowly so as not to cause gas (similar to flour vs wholemeal flour in humans) It also is bulkier and helps things pass through better apparently.
You may find if you add longer strands of hay into your critical care for syringe feeding it blocks the syringe. What I found best was to mix it as normal with warm water and then roll it into balls and my rabbit loved them.
Simethicone, light belly rubs and vibrations are a God send if they have gas.
We got a tiny vibrating device that was small enough for her to sit on. And she used to sit on it so I’m assuming it must have felt nice.
Here is an article quite by galens garden un the UK regarding syringe feeding and about the increased hay length being beneficial for gut motility if you can manage to get it down them. Sometimes even when syringe feeding causes gas it’s still necessary if they arent eating themselves.
“Indigestible (lignified) fibres should be at least 2.5mm in length to ensure the good gut motility essential for the wellbeing of the rabbit. Even beneficial lignified or indigestible fibre, if ground too finely, will pass through the digestive system as carbohydrate or energy as opposed to the type of fibre which acts to move the other food through the gut in a healthy manner.”
https://galensgarden.co.uk/herbivore-nutrition/syringe-feeding/
Good luck
Jade