This is essentially when new negotiation rules are introduced, or previously understood rules are changed. This is a frustration tactic and is used to gain advantage by the party changing or making the rules.
For example, there may be a bidder’s conference announced where clarification may be needed on a Request for Proposal for all bidders. Parties may spend time and money preparing for the conference, but then the conference is cancelled by the procurement team. Next, sealed bids may become unsealed and a second group of best and final bids may be announced, without refinement or clarity in RFP ambiguities. This dynamic is very common in younger procurement organizations or unscrupulous ones.
As a bidder, you must decide if you want to compete in this environment. If the answer is yes, you must pressure the opposition to stick with the original rules and understand the difficulties.