How to install a new version
Since FaLang 1.1.1 you don't have to remove previous version before installation. You just make an installation over the previous version.
The key is automatically updated.
Quickjump icon disapear
This can be a problem due to Falang not well saved in the database. Jusp open the Falang options and save it another time.
Menu are not translated
Since Joomla 3.6.1 you need to have the core system language filter plugin to have an higher priority with the Falang database driver. Since the 2.7.0 of Falang the order is done automatically.
Invalid Parent id
Since Joomla 3.7.3 a query in the assets file is no more valid with Falang , Select (1) From , this is due to a bug in php-mysql. You have to upgrade your php version to 7.+. A pull request is done to solve this problem on Joomla directly see here (https://github.com/joomla/joomla-cms/pull/17003/). The fix in the request work perfectly.
Since Joomla 3.8.0 the line 111 to change is in this file libraries/src/Table/Asset.php
Infinite loop detected in JError
The mysqi ou mysli (Falang) is activated but your host don't support mysli connection.
You have to change manually this in configuration.php
You have to change the line
public $dbtype = 'mysqlix'
public $dbtype = 'mysql';