You can build a constructed list to control the block randomization and you shouldn't need any skip logic. Create a predefined list (I'd call mine BlockList) with three items. The label of each list item is irrelevant since the list isn't actually shown in any question, so I'd just use 1/2/3.
Create a constructed list (BlockListRandom) and then set up constructed list logic to add items 1-3 based on some other question. If it was a simple case where, say, Q5 had 3 check boxes and controlled what blocks to see, you could do something like AIC(Q5). You could also toss in any list instructions like
which would add anything chosen from Q5, randomize the order, then trim it down to at most 2 of the 3 items.
Then in the randomized blocks area, you would use the dropdown box to select BlockListRandom as the controlling list for your 3 MaxDiff blocks. The end result is that if list item 1 is in BlockListRandom, the respondent would see the first MaxDiff exercise. If not, the first exercise would not be shown, no skip logic required.