You'd need to provide an example if you want an objective answer. While it is possible that speakers mumble (as per Bill's answer), if you the listener are not used to the difference between a "sh" and a "tch" sound, you will probably think that "watched" sounds like "washed". That is, it's possible you also misheard.

It is possible as people can mumble. I say "watched" the tch sound is very clear

Don't say it that way yourself. It's not normal, correct, careful English. A teacher or a news broadcaster would not say it that way. And it's not a normal informal pronunciation, either. There are many, many regional and personal variations in pronunciation. Saying "watched" as "washed" isn't familiar to me, but it might well be a regionalism. In the central part of the country it is very common to add an "intrusive R" to words like "wash" and "Washington." People from other parts of the country hear this pronunciation as "warsh" and "Warshington." In some places it is common to add an "R" on to end of words that end in a "-uh" sound. The late President Kennedy always pronounced the name of the country "Cuba" as "Cuber." In New England, particularly Boston, the "R" sound becomes almost like an "ah" vowel sound and almost vanishes. The standard joke is "I pahked my cah in Hahvahd Yahd" (for "I parked my car in Harvard Yard.") Some English words involve difficult tongue acrobatics and are often slurred or simplified. The word "nuclear" is often mispronounced as "nucular"--notably by former President George W. Bush, but it is very common.