QlikSense - Search within apps produces an "internal engine error"

A customer reported a case where searching within apps produced an "internal engine error"

The issue could be reproduced in their environment with different specific search strings in different apps, and seemed data related (all the apps shared some common data)

In the logs we could find errors like this:
594 23.3.1.0 20181115T074439.880+0000 ERROR QS-Main 4d0beac2-0bca-4884-ac8c-a6d9dde12e1c 20181115T074439.879+0000 12.212.4.0 Command=Doc::SearchSuggest;Result=-128;ResultText=Error: Internal error a3105553-e5e8-4c42-b293-c11e63b23eee c70397db-1c55-44f1-82a8-8d7d46979981 31 QS-MAIN administrator d3105b0b-d2a3-4dfb-989f-71f1f4a6ada3 f044a90c-9b9a-467d-b66b-dadecda2ba5b test Engine Not available Doc::SearchSuggest Doc::SearchSuggest -128 4d0beac2-0bca-4884-ac8c-a6d9dde12e1c594 23.3.1.0 20181115T074439.880+0000 ERROR QS-Main 4d0beac2-0bca-4884-ac8c-a6d9dde12e1c 20181115T074439.879+0000 12.212.4.0 Command=Doc::SearchSuggest;Result=-128;ResultText=Error: Internal error a3105553-e5e8-4c42-b293-c11e63b23eee c70397db-1c55-44f1-82a8-8d7d46979981 31 QS-MAIN administrator d3105b0b-d2a3-4dfb-989f-71f1f4a6ada3 f044a90c-9b9a-467d-b66b-dadecda2ba5b test Engine Not available Doc::SearchSuggest Doc::SearchSuggest -128 4d0beac2-0bca-4884-ac8c-a6d9dde12e1c

Environment:

Qlik Sense September 2018

Since the customer was not willing to share the source data with us, we could not reproduce the issue in our environment and investigate further.
The workaround, in this case, was finding which fields contained the strings that triggered the error and excluding those field from the search using "Search Exclude Account_UpdatedAt;" according to the help site.