UPS do not switch from battery to standard energy source

[Anonymous user]

I have Back-UPS 850 (BE850G2-RS). When I put my computer into sleep and turn off the energy source, it switches to battery power as it should. When I turn on the energy source back, UPS powers on the computer but do not switch back from the battery to the standard energy source. As a result, the computer shuts down again (not gracefully). Only after that UPS is switching to a standard energy source. 

If I turn off the energy source while the computer is not sleeping, PowerChute shutdowns it gracefully. When the energу source is back computer does not start again, and UPS is switching from the battery normally.

The Hibernate mode is disabled.

How do I fix the first case and make UPS switch back to the wall when the power is back? Could it be a defect and I should visit a service?

[BillP]

@Anonymous user 

When the UPS switches to battery power, it will remain running until the battery is depleted or until it has been commanded to power off. When a computer is running PowerChute, you can configure PowerChute to keep the computer on as long as possible or preserve battery power. In either case, once the threshold has been met, PowerChute will begin the shutdown of the OS. At the same time, PowerChute sends a power-off signal to the UPS. The UPS will wait two minutes and then power off. If AC has been restored during the two-minute delay, the UPS will remain running on battery power. Once the two-minute delay has elapsed, the UPS will power off, wait 6-8 seconds, and power back on.
If you are switching the AC back on before the UPS shutdown process completing, the computer may restart and then shut down again when the UPS cuts AC to complete the process.