Opt out of optimized fixed CPM bidding.
By default, DV360 optimizes bids to bid as low as possible. This is a default setting in DV360 made at the partner level called Optimized Fixed CPM Bidding.
Kargo recommends opting out of this setting for your advertiser. When this setting is enabled, the optimizer will attempt to bid as close to the floor price listed in the Inventory tab as possible. This will sometimes cause bids to be lower than the actual floor (due to other fees).
If opting out of that setting is not an option, you should bid at least a few dollars above the floor price (recommended $4-5 above floor price) to ensure minimal to no bids fall below the floor price.