Hello dear Matomo team,

We have an app that tracks accesses in the app via the Matomo-iOS SDK.
However, for some time now we have noticed that this no longer works:
The request sent by the app is answered by the Matomo-Server with an HTTP error 500.

The corresponding request that the app sends to Matomo.php looks like this:

{"requests":["?idsite=6&rec=1&ca=1&_id=D10C88C12F424F8D&uid=F51DE671-042E-4294-90BD-96F34E9AD3BF&_idvc=3&_viewts=1651760503&_idts=1651753480&url=http:%2F%2Fxx.xxxx.xxx.xxx. xxxx%2F&action_name=&lang=de-DE%3Bq%3D1.0&h=07&m=09&s=04&cdt=2022-05-06T05:09:04.626Z&res=375x812&e_c=Aufrufe%20von%20Bildschirmen&e_a=ViewScreen&e_n=Dashboard&dimension1=2492&dimension2=3.4.1"]}
The result is then a: HTTP Status Code 500 Internal Server Error.

The request is compiled by the Matomo iOS-SDK.
However, this problem can also be reproduced using Postman.

If we modify the request parameter lang=de-DE%3Bq%3D1.0 to lang=&lang=de-de%3Bq%3D1.0 it seems to work.
Interestingly, the subsequent trackings also work, even if they use lang=de-DE%3Bq%3D1.0 again.

In our opinion, this is a bug in the Matomo server.

Matomo-Version: 4.9.0
MySQL-Version: 10.5.8-MariaDB-1:10.5.8+maria~focal
PHP-Version: 8.0.18
Server Operating System: Linux 8e0c805a09ed 4.15.0-176-generic #185-Ubuntu SMP Tue Mar 29 17:40:04 UTC 2022 x86_64 Linux

We have anonymised the iP-addresses on the Matomo server.
The location recognition system is set to Standard.