EC GET breaks sometimes

[cthulhu-rider]

defects of #3996

1. SN can respond w/ incorrect payload of EC object
2. SN shutdown can hang after EC GET requests
3. following errors sometimes occur

part#1: /dns4/localhost/tcp/8084: parse ID (nested message) field: parse value (bytes) field: parse field #1 of LEN type: unexpected EOF

part#1: /dns4/localhost/tcp/8084: handle meta header: parse version (nested message) field: wrong type of field #1: expected LEN, got VARINT

Possible solution

1 and 2 are just code mistakes., i already found a solution

3 is not yet clear. Code seems ok overall, and it happens inconsistently. Local debug revealed dependency on the concurrent requests. Isolated errors begin to pop up at ~90-100 threads. After that, a more or less linear dependence errors<->routines is observed

Steps to Reproduce (for bugs)

load testing

i'm using EC 4/1 policy and sending GET requests to one of container nodes

Regression

yes