FB Platinum flying on a MU/FM business class ticket and transiting in PVG T1; inbound on MU and outbound on FM and it will be vice versa on the return. I had access to the No. 36 lounge, which is the MU/FM lounge and includes KLM on the signage. Nearby is the No. 39 lounge, which sign-posted for AF. The SkyTeam Lounge Finder does not name it like this.
As the No. 36 lounge is quite grim (layout, seating, food, no view) so not wanting to whilst away a significant transit duration there, I went to try the No. 39 lounge using my FB status and holding SkyTeam business class boarding cards. I was told by the receptionist, after presenting my boarding cards* and FB digital card, can only access if on the AF flight and not other SkyTeam flights and to go to the No. 36 lounge instead. I never noticed the No. 39 lounge on my previous MU/FM business class transit and thought it might be nicer to pass a few hours.
Is lounge hopping not allowed by SkyTeam like you read about for oneworld and Star Alliance status holders; many reports of OW and *A lounge hopping in LHR T3 and T2, respectively.
*It's irrelevant but my boarding cards had the KL logo because they were printed in AMS which was the start of my MU/FM ticket - if they had the AF logo and I'd started in CDG, who knows.
36 is MU's, so standard ST access rules
39 is ran by the airport, so not standard ST rules, but AF has additionally contracted it (I would say 39 is better)
But the MU's flagship lounge is 137 in S1 (5min train shuttle), standard ST access rules