Yeah, it's not normal... My code specifically checks for tradables that were marked as being imported automatically from BVG. It will never remove anything that was entered manually here. BTW, I'm seeing 380 tradables in your list... Are you sure you're talking about tradables?
Either way... I usually wouldn't shoot myself in the foot willingly, but still, I would suggest you export your tradables to BVG format (there's a tutorial for that because there's a learning curve), then import them over there, and you'll probably have more potential trades. Lestrade's never reached the number of users needed to make it sustainable as a trading site (I was really hopeful for that back in 2017, but I've moved on from that), so I simply use it myself as a clearer, cleaner way to manage my tradables (which were all entered here and never deleted automatically), since BVG is targeted towards trading and not maintaining lists in a friendly way. Then I occasionally export them to BVG to get offers.