I would just do a series of high enemas with plain warm water, first about a third bag to cleanse, then the rest, then try to get as much as you can in, holding for as long as possible. Maybe even another full bag after that.
I have had the same thing happen. I always try to analyze what's going on. With me, I have noticed that when I may have been dehydrated, the enema is absorbed, and harder to expel. A series of plain, warm water cleansing enemas always seems to help after that.
I know that some will caution the use of high enemas due to depleting the good bacteria, but our bodies will replenish this in time on it's own, or you could add a probiotic capsule to the last enema if you want.