In the past year at Globevestor, I have closely witnessed a few instances of startup fundraises where key investors behaved un-admirably, by failing to honor their commitment or trying to re-negotiate previously agreed terms of investment at the last minute.
Mostly this happened at the round closure stage, i.e. post term sheet/ due diligence & during paper-work/ money transfer, despite the investors being well aware of the limited runway & options available to the startup. At worst, they possibly happened specifically because of this knowledge!