As a non-native learner, I can’t say for sure, but I think /l/ in “All that” can be assimilated to /ð/ and realized as a dental lateral approximant.
This is a quotation from “An Introduction to English Phonetics” by Richard Ogden:
2.5.3 Dental Dental sounds involve an articulation made against the back of the upper teeth. [θ ð] in English (as in the initial sounds of ‘think’ and ‘then’) are often dental; they can also be interdental, that is, produced with the tongue
between (‘inter’ in Latin) the teeth, especially in North America. Dental forms of [l] and [n] are used in words like ‘health’ and ‘tenth’, where they are followed by a dental; and dental forms of [t] and [d] are
regularly used in many varieties of English (e.g. some forms of Irish or New York English, and in Nigeria) as forms of [θ ð].