did you clean the db tables before uninstalling?
In later JEM versions there is a setting for that (see image). If not, you have to do it manually.
on JEM 2.3.0+ stable in latest Joomla (3.9.25) Protostar php7.4.15
Personally I use t4_stark template with t4_system plugin framework with bootstrap and fontawesome)
(I prefer free "Signal" or paid "Threema" instead of "Whatsapp".)
I'am not shure, when the error occurs.
Does ist show up when you install JEM 2.1.6 or at which point you get this error message?
It sounds for me that some install/uninstall routine forgots to delete the table with the name shown in the message.
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