I hear there might be equipment delivery delays for traditional build sites (not PSU builds). Possibly related to Buffalo retooling to v3, but that's just speculation. Also once trench work and conduits are in place there are typically inspection requirements before concrete can be poured - so that might be part of it too.
It's also possible that the distance between jobs underway and number of jobs active is factoring into this, but also speculation. I know the large Canton 20 stall + solar canopy site is underway and possibly competing for contractor resources. Most of the other sites I know of for this company are in various states of 90%+ done holds (Lowell, Framingham, Lynnfield, Foxborough, Provincetown, Southington CT). With only Canton & Lawrence with significant work underway, I wouldn't be surprised if we learn of a new site beginning construction any day now...