Okay, the amount of overlap between the 2 problem frames is only 7% of the height dimension. That’s pretty low.
And if I try to register them to each other, it works fine if I choose
St-avg-9000.0s-WSC_1_3.0-x_1.0_1.0_dr-sqr-full-qua-add-sc_BWMV_nor-AA-RL-MBB5_2ndLNC_it3.fits
as the reference, but if I choose
St-avg-7200.0s-WSC_1_2.0-x_1.0_LZ3-ref-qua-add-sc_BWMV_nor-AA-RL-MBB5_1stLNC_it34.fits
as the reference it fails. So this is a problem in the pattern recognition engine which I’ll try to fix.