Flaky subscribe test

[kuznetsss]

Issue Description

Sometimes there is a test failure in CI:

13> #115 failed: Subscribe_test.cpp(1053)
/usr/local/include/c++/15.2.0/bits/stl_vector.h:1370: constexpr std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::back() [with _Tp = std::tuple<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, int>; _Alloc = std::allocator<std::tuple<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, int> >; reference = std::tuple<int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, bool, int>&]: Assertion '!this->empty()' failed.

An example of such failure in CI.

Steps to Reproduce

It's not obvious so far how to reproduce this, but it looks like the failure happens when using gcc 15 on Linux in debug more with code coverage.

Expected Result

Test passes.

Actual Result

Sometimes test fails.