For Logic to keep the tempo changes from the tempo fader, Logic needs to record them.
IOW, on its own, Logic will follow the tempo map that is already recorded.
Therefore one has to proceed as documented
, and also enable the tempo changes option in the project recording settings (as mentioned in my previous post).
Otherwise, the tempo fader actions won't be permanent, as you experienced it.
LogicPro 10.6.2, MainStage3.5.2
MBPro 17", Core2Duo, 8G, OSX 10.12.6
MacPro, Xeon 6Cores, 64GB, OSX 10.15.7
ULN8, MOTU MIDI TP-AV, C4, MCU Pro, KorgNano, Novation SLMkII
AAS, NI, Celemony, Spectrasonics, Korg, Arturia, etc...
PC, iPad3(V-Control & LogicRemote), AtariST(Notator SL), Several vintage gear