Smart-UPS SRT 5000 delivering some alerts, and not delivering others

[Anonymous user]

Hi there! 

Description of the problem:
During the last weeks a couple of power outages occurred and we expected that the UPS would report them, however we received no alerts about that. When I went to check the logs, the events do appear there. It's just that we are not receiving them.
We do receive some events though, such as:

    -UPS: RFC1628 MIB alarm entry removed.
    -Web user 'XXX' logged out from 10.X.X.X. (I replaced the real values with x)
    -UPS: Self-Test passed.
But we don't get most of the alarms we care the most, like:
    -No longer on battery power. 0x010A
    -An input voltage or frequency problem no longer prevents switching to bypass mode. 0x0210
    -Bypass not in range ; distorted waveform. 0x020F
    -On battery power in response to rapid change of input. 0x0109
    -On battery power in response to distorted input. 0x0109

Example of the issue:
Take for instance the events (event.txt attached) corresponding to 24/08/2021: There was a power outage but none of the messages in the logs were sent to our Distribution lists, but instead on 24/08 we just received a couple of RFC1628 alarms. 

I already tried:
-I already checked networking paremeters (including SMTP and DNS parameters) and they seem ok. Some events are being sent so I don't think the problem is here anyways.
-The events configuration (Configuration>Notification>Event Actions> By group/ By event) is the same in [UPS: RFC1628 MIB alarm entry removed] and, for example, [On battery power in response to rapid change of input. 0x0109] (evidence attached). In other words, recipients in the events configuration are the same for Informational, Warning and Critical events.
-I changed the SMTP server from hostname to IP, just in case.

About the UPS:
Smart-UPS SRT 5000
Firmware Revision:
UPS 04.7 (ID1013)
APC OS (AOS) / Application Module version:
v6.5.6

Conclusion:
Some alerts are being delivered to our Distribution lists, and some others are not.

Do you have any clue what may be happening here?
Thanks!
M.