Recent data prints:
Fight is considered "clean" at FRA in both directions and transfer security is not needed. Be very careful when exiting the jetway to take the path for continuing SQ passengers. NOT connecting. Go no further and ask if necessary.
AC lounge initially would not accept my BP SIN>JFK for access as it did not indicate originating at Frankfurt. Really? Took an AC colleague to enter a manual admission.
That's a common occurrence at the AC lounge — SIN-JFK BPs don't scan and they have to enter it manually. They should be pretty familiar with the issue though (although a lounge agent did try to deny me entry once after my JFK-SIN BP didn't work by claiming I was in PY until I helpfully pointed out the *G printed on it), but an easy workaround is asking for different seats for each leg at check-in so you get two BPs.
Also the showers at the MLL are nicer than in the LH lounges but IMHO the breakfast food at the LH SEN lounge has gotten much better (and you can get decent espresso drinks at the bar) so I find myself heading there instead nowadays.