The following wording from the German Foreign Office:
Travel to the provinces of Narathiwat, Yala and Pattani as well as parts of Songkhla in southern Thailand is strongly advised against.

Terrorism

The worldwide danger of terrorist attacks and kidnappings remains unchanged. In Thailand, too, attacks cannot be ruled out even in holiday areas. Most recently, there were small bomb explosions at various locations in Bangkok on 2 August 2019.

In the provinces of Narathiwat, Yala and Pattani, as well as parts of Songkhla in southern Thailand on the border with Malaysia, there are regular clashes between separatist groups and security forces, as well as terrorist attacks, including on targets frequented by foreigners. Emergency laws are in force there. In some districts, especially on the border with Malaysia, night-time curfews may be imposed at short notice.

Be especially alert in busy places and on special occasions.
Always follow the instructions of security forces, even in the event of night-time curfews for unavoidable stays in the southern provinces.
Heed the worldwide security advice.