Might need to re-visit chain length if after correcting the DR height you still have the chain fall off occasionally. I usually would expect too long a chain having slack in some gear combo's to be more prone to falling off the front.
Chain length will be low on my list of other things to check normally for dropped chains. I only bring it up because you said you lengthened it.
Shimano rear DR? They tell you how to size the chain in their DM's for that model DR.
https://si.shimano.com/