Any examples of a policy issue on which a patterned conception of justice might plausibly disagree with a historical entitlement based conception of justice
This account might help ('ASU' refers to Anarchy, State & Utopia) :
Nozick defines a patterned principle as a principle specifying that the distribution of goods "is to vary along with some natural dimension" (ASU 156). Natural dimensions are basic qualities of the person, such as need, desert or talent, that are identified by the principle as exclusively relevant to the determination of just shares in the distribution of goods. To each according to his need; to each according to his desert; to each according to his ambition and effort; to each according to his marginal product - these are all patterned principles. While Nozick concedes that he fails to furnish "a general criterion" (ASU 156) for identifying natural dimensions, he provides numerous examples of the pattern-variables that define such dimensions. In addition to need, desert and effort, Nozick mentions moral merit, I.Q., marginal product, "the weighted sum of the foregoing, and so on" (ASU 156-57). Each pattern-variable represents a general quality of agency, and may therefore be employed to evaluate the status, relative to claims of distributive justice, of (virtually) any person.
Patterned principles of distribution are inconsistent with respect for entitlements, Nozick argues, because maintaining a pattern requires "continuous interference with people's lives" (ASU 163). Nozick offers the notorious Wilt Chamberlain thought experiment to illustrate this claim (ASU 160-64). In this example, the initial distribution of social goods conforms to D1, a just pattern under our preferred patterned principle. Chamberlain then negotiates a contract guaranteeing him a fixed royalty from tickets sold. At the end of the season, Chamberlain is rich - and D1, the original patterned (and just) distribution, has been upset. In order to preserve DI, Nozick argues, society would have to (i) prevent people from transferring their legitimately acquired resources as they wish or (ii) continually and intrusively redistribute resources.
In his general discussion of patterned principles, Nozick has described the defining quality of patterning: patterned principles privilege a particular natural dimension as the sole consideration relevant to distributive justice, so that the justice of a distribution of goods may be determined entirely through attention to this dimension. The Wilt Chamberlain example, however, exhibits a second basic quality of patterning: patterned principles establish a unique schedule of just distributive shares which must be maintained strictly in order to preserve justice (ASU 157). The Wilt Chamberlain example is problematic precisely because the distribution of goods will predictably depart from the strict schedule of distributions established by DI1. Patterned principles, therefore, do not merely establish a relation between a pattern-variable and justified claims to goods; they establish a literal and fixed relation. (Alexander Kaufman, 'The Myth of the Patterned Principle: Rawls, Nozick and Entitlements', Polity, Vol. 36, No. 4 (Jul., 2004), pp. 559-578: 561-2.)
Nozick believes that we have the natural right to acquire property under certain conditions. Whatever I acquire under those conditions is a just acquisition. Equally what I transfer to you under certain conditions, is a just exchange. There is no guarantee - quite the opposite - that the distribution of property that results from just acquisition and just exchange will satisfy the distribution required by some social ideal of justice. 'To each according to their needs', for example. Such an ideal desiderates a distribution of property in which, regardless of our just acquisitions and just exchanges, each person has property according to their needs. Property possession under this ideal of justice will exhibit a pattern - exactly this needs-based distribution.
As mentioned above, it is very unlikely that a distribution resulting purely from just acquisition and just exchange will produce any such distribution - will embody any such pattern. To impose or maintain this or any other kind of pattern, Nozick argues, as summarised in the quote, society would have to (i) prevent people from transferring their legitimately acquired resources as they wish or (ii) continually and intrusively redistribute resources.
Whether we do have rights of acquisition and transfer, and if so under what conditions, are matters of controversy, as is the justice of redistribution. I make no comment on these matters as they extend beyond your question.