ravel wrote:susser 2.5 needs "Simple Forcing Loops" and/or "Comprehensive Forcing Chains" for the 3 puzzles, which (in general) cannot be expressed as xy-chains.

Susser 2.5.4 used "Simple Forcing Chains" (xy-chains) to solve these, not the other types of chain. The strategies Susser reported it used are listed in my posting! (I suspect you've not de-selected the other "advanced methods" in Susser's list of allowed "Heuristics".)

ravel wrote:xy-chains are bivalue/bilocation chains that always start in a bivalue cell with candidates xy, showing that a y in the cell would lead to an x in another one, so that either of the 2 cells must hold an x. Then x can be eliminated from cells that see both.

It's an inessential matter of terminology whether the cell in which an elimination occurs is regarded as part of the xy-chain. If we do so -- as Susser's "Simple Forcing Chains" do -- then each chain eliminates just one candidate, and there may be more than two candidates in that cell. (But this is not relevant to the point of my posting.)

ravel wrote:Only Simple Forcing Chains (bivalue chains with contradiction) always can be expressed as xy-chains.

And that is what Susser used to solve these.

EDIT(1): Added comment on selecting Susser's allowed solving-methods.

EDIT(2): Added comment on Susser's terminology for xy-chains.