That's not collusion. Collusion requires a secret agreement between two parties to defraud a third party. One party unilaterally deciding to copy another party, regardless of the end affect, is not collusion. Causing market prices to rise is not illegal, so long as you don't do something illegal to cause them to rise.

Now it's possible that there was some separate agreement, for example Amazon and a competitor may have both agreed to raise a price some percentage and then they made small adjustments to look like it was just an automatic response. But the fact that algorithm seems to have accidentally lowered prices on some occasions would seem to suggest it genuinely was acting unilaterally. Or perhaps those failures were a deliberate part of a larger ruse. Ultimately it will be for a jury to decide but the FTC has its work cut out for them.