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There were multiple disks with read errors:
May 1 16:53:20 Monstruo kernel: md: disk4 read error, sector=6445062760
May 1 16:53:20 Monstruo kernel: md: disk4 read error, sector=6445062768
May 1 16:53:20 Monstruo kernel: md: disk4 read error, sector=6445062776
...
May 2 01:52:39 Monstruo kernel: md: disk15 read error, sector=588559224
May 2 01:52:39 Monstruo kernel: md: disk15 read error, sector=588559232
May 2 01:52:39 Monstruo kernel: md: disk15 read error, sector=588559240
and then disk9, disk4 and disk15 look more like a connection/power issue, replace cables but also run an extended SMART test on disk15 since it's showing some issues.
As for disk9 it dropped offline, so there's no SMART, check/replace cables and post new diags.