How long will soaked chia seeds last?
Chia seeds have been known to harbor salmonella, and considering their high fat content, high carbohydrate content, and their physical/chemical reaction to being soaked in water, they are an ideal growing medium for any number of hazards.

The USDA does not have a published opinion on the topic.

The EFSA has approved them as an ingredient in all forms,including uncooked, but has only researched cooked form (which is typical for seeds and nuts)

Give the lack of guidence from a credible organization, and the wildly varying ranges of unauthoritative sources, I would treat soaked chia seeds as most akin to leftovers of a salad that has dressing applied, which is to say even in the refrigerator, no more than a day and "when in doubt throw it out".