I have written about this elsewhere. My seedlings can be up to 9-10" and luxurious. Then they just topple over because no roots are attached anymore. These topples all occur in a raised bed that has been a very successful vegetable garden. Recently, I might have saved at least 2 from nearly 30-odd topples by treating them similar to proliferations: trimming the leaves and putting them back in soil - elsewhere.
The experience has been disconcerting and it continues. At the moment, I am watching three about to flower for the first time. I can see, however, they will topple soon just be feeling how wobbly they are in the soil.