I found that if I am reading the RVR 1960 version and then add a verse to the memorization module, it shows up in the memorize list but when I click it to start the module, the verse is empty. I have to add the verse with some other version (I've tried with KJV), and then I can switch to RVR60 and I can train in Spanish.

This is confirmed. Non-English book names are causing this. Thanks for the report.

Also, there is a problem with the RV60 itself: some words are stuck together, e.g. Prov 5:3-6 has some examples. This causes the memorization module to sometimes consider two words as one.

One more :)

The 1st letter scramble test breaks if the first letter of the word has an accent, which is common with the RV60 translation.

Yes, we really never tested memorization with non-English volumes. We'll get there, though!