Do you think that using some swap space in my Pi would do the trick? In this way I would have enough memory to create the DB directly on the Pi.
Also I don't think the meta entries for LMDB are even the same going from 64 to 32 bits. It's typically bound to the pointer size, which naturally differs between 64 and 32 bits.
Yup! I saw that it complains about some .lmdb files are not LMDB format...