What is the normal rate of failing to submit a block from Electroneum pool?

[sunnyrat]

We have a node-cryptonote-pool mining Electroneum, and sometimes it even finds a block .  However, due to many factors, most of which are obscure for me, it fails to submit it, fails with error like this:

Error submitting block at height 141295 from [email protected], share type: "trusted" - {"code":-7,"message":"Block not accepted"}

Sometimes it just does not have this block:

{"code":-7,"message":"Block not accepted"}

The electroneumd (fork of monerod) shows error:

Transaction not found in pool

at the same time. We lose ~50% of mined blocks with such errors. The question is, what is the normal rate for such errors? Is 50% indeed normal and what we can do is just to give up and live with it, or there is a room for improvement?