Jarring clunk into first gear - sometimes

I have a 2014 Chrysler Town and Country with 76K miles. The transmission works properly most of the time. No problems shifting through the gears. Usually OK from stationary into reverse or forwrd gears. Except, occasionally, there is a jarring clunk into first gear. After the jolt, everything is OK. I haven’t been able to determine any pattern to when it occurs-it seems pretty random. Of course, I can’t check the transmission fluid as there is no dipstick and access under the vehicle is limited. Has anyone had a similar issue or have an idea of how big of a problem this might become?

Tester