This article provides some insight into the recent diplomatic tensions between Lithuania and China:

Taiwan announced the new mission last month, saying it would be called
the Taiwanese Representative Office in Lithuania, the first time the
island’s name has been used for one of its offices in Europe, as
normally only “Taipei” is used.

Taiwan took part in the Tokyo 2020 Olympics under the name of “Chinese
Taipei”.

Lithuania’s permission for the office to open under the name of Taiwan
was done “in disregard of China’s repeated representations and
articulation of potential consequences”, and severely undermines
China’s sovereignty, the Chinese Foreign Ministry said on Tuesday
AEST.

According to Wikipedia there are several dozens of countries that have more or less official relations with Taiwan/Republic of China, but all but the representative office in Somaliland took care to avoid "Taiwan" in their official names.

I am wondering why Lithuania broke this rule especially that European Commission seems to acknowledge that Taiwan is not a sovereign state (example below):

the EU Commission referred Taiwan as a "separate customs territory,
but not as a sovereign state", highlighting the role of Taiwan as
autonomous economic entity for the purposes of the establishment of
relations with the European Union.[4]