Why does the share price of some companies fluctuate when there is no bid or offer price?

we can only think that there is some off-market transactions that get reported to the exchange. So there might not be active bids and offers but there are transactions being made and reported to the exchange.

It’s common practice for large institutional managers to get the broker to find the other side of their trade in smaller stocks rather than placing live orders in the market. Once the broker has both sides and they have agreed a price and volume the broker puts both sides (at the same time) through the exchange to effectively report the transaction.

This is effectively the function dark pools are starting to automate, rather than having the broker manually find the other side.