Sorry it took me so long to respond. I was away working for the past 2 weeks.
Any luck yet?
The crottin issue you are describing with the slipping skin is usually related to moisture. Here are probes to look at:
1. Not drained enough or not pre-drained in the first 24-48 hours = too much moisture in the cheese
2. Too much humidity in the aging container for too long (also could happen if not drained enough as mentioned in #1 above). That could cause an over-growth of the soft geo skin and lack of blooming of the dry velvety PC mold
3. The milk... I am taking a break from Goats cheese for 3 months. It's just bad in the northeast this time of year. Many goats are dry and the goats that milk rely on supplemental food because there is no grass for them to graze on. This results in badly behaving milk with unpredictable results. (does anyone else out there feel this way? Remember we are in the north east, not in sunny California)
4. Not enough salt means not enough osmosis to get the whey out and not enough control over the Geo so it grows out of control. That could also explain a flavor that isn't balanced enough (more sour, less salty)
If the flavor issue was bitterness than you may have put too much rennet in. If this is true, it can also explain also why you would have so much moisture trapped in it (rennet gels the milk and eventually build these walls around the curd that trap moisture in. You don't want hard curd here because you need the moisture to go away). Remember, this is a semi lactic cheese, not rennet coagulated. 3-4 drops rennet (1/16th teaspoon) to 1 gal milk is what you need. Not more.
The excess moisture that cause the slip skin may also be related to a cheese that is too large and trap too much moisture in the curd that fails to come out before the outside is done aging, so size does matter here.
As I said many times before here, this kind of cheese should ideally be aged on hay (as soon as it blooms and is not too moist). the hay gives is a nice barnyard quality and it wicks the moisture out of the curd.