4 sourced reports, with what to check before you buy. Each one links to the page it was reported on.
Costly or dangerous
Mainboard replaced under warranty after heavy freezing
Found via 'Lenovo Tab M11 problems review' (Comfy.ua customer review).
What to check. A buyer reports the tablet started freezing heavily a few months after purchase and needed boards replaced under warranty, so a hardware fault is possible within the first year.
Tablet slows down and cannot handle two apps at once
Found via 'Lenovo Tab M11 problems review' (Alza.cz customer review, Czech market).
What to check. A verified Czech buyer reports the tablet slows down a lot and cannot handle two apps at once, so multitasking performance is a real limitation for this entry-tier model.
Tablet stops connecting to Wi-Fi after powering off
Found via 'Lenovo Tab M11 sorun şikayet' (Comfy.ua customer review).
What to check. An owner reports the tablet stops connecting to Wi-Fi after it powers off; a factory reset fixes it temporarily but the problem recurs, pointing to a Wi-Fi module fault.
Found via 'Lenovo Tab M11 reliability review forum' (Galaxus.de customer review, German/Swiss market).
What to check. A Galaxus buyer notes the tablet freezes and takes very long to restart after a complete discharge, so letting the battery fully drain should be avoided.
These reports come from the pages linked under each item: owner forums, repair guides and workshops. They are not a diagnosis of any one unit, and a careful check of the one you are buying still applies.
Text from the Kriko Tablets catalog, version 0.1.1, under the CC-BY-SA-4.0 license.