Why is the Power Factor 60% ? That might be true of a lightly loaded AC Motor. But an efficient Computer (or Electronic) Power Supply should be much better than 60%.
Possible answer on review of specifications:
http://www.trv.com.ar/detalle-shop.php?cd=11
Power Factor 60% measured at Input not Output meaning it is
inefficient.
70% static ongoing load should be OK for a high quality UPS.
Check the waveform of the UPS (look at the documentation). A good UPS will have a good sine wave output. Cheaper UPS units have a hash waveform that the manufacturer claims approximates 117 volts RMS (or your country's nominal voltage). At 70% load, the voltage may not be correct. You need a (digital) voltmeter to check this point.
Note: Specifications say the UPS shuts down if overloaded. It may be tripping up your computer. Try reducing overall load to 50% or a
bit less.
The specifications also say it is a hash output waveform.
Is this a bargain basement UPS? Cheap electronics tend to provide what you pay for, so be cautious about this point.
Is the UPS under warranty? If so, return for replacement or warranty service.
The situation is NOT normal. My Desktop is on UPS (and has been for years) and never reboots when the power fails and the UPS kicks in, or just connected to the UPS.
Check your computer on your home mains and not on the UPS. If it works OK that way, then the UPS may need service.