Upgrade To Flexicontent 4.2.1 failing

Dear, 

We get the message: internal server error when updating from flexicontent 3.3.2 to 4.2.1
After refreshing the page, we get update successful but we are troubleshooting where the internal server error comes from.
Apparently the error came from set re-index needed flag to fields... there we get no return in the log.

The query below has 31820 as count.. 

$db->setQuery('SELECT COUNT(*) FROM #__flexicontent_items_ext LIMIT 1');
$has_items = $db->loadResult();

What can we do in order to avoid the internal server error.. It is a big site with >10000 articles.

See here the dashboard.

Updating installation Upgrading from 3.3.2 to 4.2.1
Log : Additional extensions Log : Upgrade tasksTasksStatus Delete orphan plugin entriesno changesEnable FLEXIcontent system pluginsno changesConverting deprecated fields types: 0hidden   0relateditems   0relateditems_backlinks   0sharedaudio   0sharedvideo   0extendedweblink  
1minigallery   , uninstalling plugin: success

38groupmarker   , uninstalling plugin: successConverting old field parameter names to new names  Upgrading DB tables (adding/dropping columns):table(s) upgraded: 2Create/Upgrade advanced search index table:nothing to doCreate/Upgrade authors configuration DB table:nothing to doCreate/Upgrade reviews DB table:table(s) created / upgraded: 3Create/Upgrade media data DB table:table(s) created / upgraded: 1Create/Upgrade content cache DB table:nothing to doCreate/Upgrade DB tables for downloads enhancements:table(s) created / upgraded: 1Create/Upgrade layouts configuration DB table:nothing to doCreate/Upgrade fields DB table:nothing to doSet re-index needed flag to fields
 

hello
1 maybe update to last 3.X series 3.3.11
2 i didn't have any error on this update maybe its a server limitation (time out or other)

Update to 3.3.11 was successful, updgrade to 4.2.1 is failing

Try to actived débug and error reporting before update to sée more return