What do the stars look like when you take the system out of focus like for a focus run?  Are they nice concentric circles or do they go from round to oval to any one of a number of shapes?  This can be a rough look at seeing.  The type of seeing can do different things (high seeing like from the jet stream to local seeing from heat rising off of a building).  If you are imaging through a river of moving air, you are likely to see this in your images.  If your system has returned round stars consistently, and all of a sudden it doesn't then something has changed.  If you haven't moved, adjusted, screwed with the imaging train or instrument, changed software settings, anything like that then seeing can be a potential culprit.  If the system has struggled to return round stars and the issues you described are not new, then there is another issue and differential flexure is a likely suspect.  If the jet stream is overhead with that river of fast moving air, seeing will likely be poor.