Recently I've seen the SQZ SHG PZT bottom out (reaching < 1V) during regular operation. I don't think this is a huge problem: I did not notice the low PZT operation add much extra noise to our loops (checked OPO_TRANS and OMC_TRANS here). Though I did take the opportunity to tweak up our OPO_ISS loop, we are now using both boosts (in guardian too). 

When SHG PZT ran out of range ~0V, SQZ_MANAGER handled it as expected: the squeezer lost lock, got out of IFO, and relocked itself. So, seems like it is fine for SHG PZT to bottom out: it doesn't inject lots of extra noise, and squeezer will auto-relock once it's down.