It is not really possible to know exactly what caused this, but you can try various combinations of the TECH= and RIDGING= options. You could also try using the FIRTH option which maximizes a penalized likelihood. Since you have a fair number of predictors, you might be flirting with separation issues, so the the FIRTH option might help. Also you could consider using a model selection method (but don't use BACKWARD). The more modern Lasso method is available in PROC HPGENSELECT.
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