welcome to GoY
Lots of questions to ask sorry!
how big is the box? and how deep is the compost?
you say you have drainage again how much and how often do you water?

as for the seed have you chosen a globe type and how long do you leave them before you pull them? they start of with a skinny root that then swells into the bit you eat.
I wonder if you are harvesting them too soon.

https://www.rhs.org.uk/advice/grow-your-own/vegetables/radishes

Lettuce takes up to 2 weeks to germinate I wonder if a slug is getting in and grazing them.

https://www.rhs.org.uk/advice/grow-your-own/vegetables/lettuce

Try germinating the lettuce indoors and hardening it off when it has its true leaves. It normally germinates quite well so perhaps the compost got dry just as the seeds were beginning to germinate but before they had appeared. Just a thought. How long did you wait before giving up on them?

You should be able to see the tops of the radishes well before they re ready for eating so no point in pulling them before that.

When someone replies to your question with more questions you can reply by putting your answer underneath s if it was a new comment. Often a bit more info will help you to get a better answer