Dark beers overcarbed

I have an issue where my dark beers(Milk Stout, Dark English Mild and Russian Imperial Stout) have become overcarbed and gush out of the bottle when I open them. The FG gravity on each of them always ended high after at least21 days of fermentation at around 65 degrees. I always justified this because I have mashed high and have a lot of non-fermentables added(oats, lactose, crystal) These are all All-Grain beers.

Milk Stout FG: 1.022
English Mild FG: 1.020
Russian Imperial Stout FG: 1.035(OG on this one was 1.110)

I don't think this is an infection issue because I have bottled other beers(Pale Ale, Cream Ale, IIPA) that have good carbonation using similar amounts of sugar(around 4 oz each). Why would these darker beers not fully ferment out and start fermenting again in the bottle? I don't have an oxygen system, are darker, fuller beers harder to oxygenate through the shaking method? Would this cause fermentation to pick back up? Any other reason?

Any suggestions/ideas why this would be happening would be great!

Thank you!

I always make sure that the FG is the same checked every other day over the course of a week.

You might want to try raising your fermentation temp to about 68-70 after about 5-6 days of initial fermentation. Try leaving just your dark beers in the primary for as much as a month if you feel up to it. Also, darker beer is typically carbed to a lower volume of co2, so maybe dial down the priming sugar just a bit.

Out of curiosity how do you clean your bottles after you pour them?
** Referring to already de-labeled bottles that you've already been using for homebrew**

The fg is always stable for more than a week before I bottle.

I will try moving my fermenter to a warmer spot a week before bottling the next time.

For bottle cleaning I always rinse the bottles right after drinking, then on bottling day I run them through the dish washer in the hottest setting then use my vinator to spray starsan in them right before infill them.

Thanks for the replies!