Hi, I have the same issue after updating to 5.1. I converted the Data Layers with commandlet mentioned here.
I tried to uncheck the “Is spatialy loaded” checkbox, but it solved only some of the problems. The better solution was to remove all actors from the converted data layers. Then it wokred both without a Data Layer and even with a new Data Layer (and its asset) created.
Give it a try and please let me know if it solved your issues 
EDIT: I noticed another problem after I exchanged all data layers for new ones. Even though I have all layers set to initially invisible and unloaded, when I render the sequence with Movie Render Queue, all Data Layers are enabled. And the MRQ is even ignoring explicitly unloaded Data Layer in the sequence (specific Data Layers are set to unloaded in the sequence)