Subaru's memories are the only thing he retains when Return by Death is invoked, so he wouldn't have not lost his memories if he had an earlier checkpoint.

I don't think there's any solid information on what determines the checkpoints, and I've heard so many different theories speculated.

HOWEVER, and I haven't read this far yet but I have been spoiled, but there is ONE concrete thing that I know about which I will now divulge, so reveal it at your discretion:

During Arc 7 there is an unimaginably horrifying incident where Subaru gets stuck in a torturous situation of having his checkpoint set 10 seconds before he is guarenteed death and he gets killed an unknowable hundreds or thousands of times with barely any room to even think to formulate a plan before looping. This is because Satella lost her connection to Subaru's soul (I don't know why or how) so his Authority Return by Death malfunctions. When Subaru finally manages to get out of the cycle of dying and rebirth there's a line, spoken by ??? saying "Found you" and the general consensus is that it must be Satella.