ILS inconsistency headache

I have read every thread on this subject and tried every suggestion.  The problem is, sometimes I get APPR lock and sometimes I don't following the same procedure each time.  I have even done touch and goes and got flight path and glide slope.  I have done so by putting the frequency into NAV2.  Flying a good intercept course, hit my preset button at which time VOR2 appears in green.  Then hit APPR.  If it doesn't lock I shut off  and restart AP until I get APPR in green at which time I get flight path and glide slope.

Now here is the rub.  I start and complete another flight and do the same procedure and cannot get APPR to lock.  I will get the flight path and the plane will turn onto it accurately.  However, the APPR does not show up so I don't get a glide slope no matter how many times I reactivate AP.  I even hit the VS button as some have suggested.  Nothing.

So frustrating when the plane has a mind of it's own and it is a crap shoot if ILS will work.

UGH!!!!!!!!!!