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

[Florenss]

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

Code:
Error submitting block at height 141295 from here-goes-wallet-address@127.0.0.1, share type: "trusted" - {"code":-7,"message":"Block not accepted"}

Sometimes it just does not have this block:
Code:
{"code":-7,"message":"Block not accepted"}

The electroneumd (fork of monerod) shows error
Code:
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?