OK, got some info and looking into that. Thanks for feedback.
looks like it was problem of my ISP-s international connection towards China...
anyway I made this morning also some improvements, and:
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Sorry, I have to make a little disconnection two times.
1) to changes DB settings for scalability - about 2-3 minutes
2) to switch stratum to another server - about 5 seconds
All settings remain same to miners and miners should resume instantly.
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