RO likely isn't the problem. Mine lowered my ph from 8.0 to 7.9 when I first installed it.
What was originally in the bucket? Did you use ammonia to clean it, and leave some residue?
When I had my coral tank, I started using the buckets the aquarium salt came in. Altho well rinsed, they still had a 'cake' of white salt adhering to the sides of the white bucket, and it kicked-up the ph to around 8. (yes, I need new glasses) Had to use vinegar to remove the salts. Just fine, now.

Did you do more than one test? What method did you use to test...strips, liquid, or pen? If you use a pen, do you have a calibration solution?
Might want to check an outdoors spiggot (or one not on the RO system) and do a side-by-side test.
Hope ya get it figured out...not sure I'd want to drink water at a 10 ph, let alone trying to adjust it for the ladies every day.