TL-MR6400 v5 LTE modem not working

That's indeed perhaps special. It is a french digicel simcard operating right now in antigua.

Thats what i found in the tech specs vor MR6400 v5:

4G: FDD-LTE Cat4 (800/900/1800/2100/2600 MHz),
TDD-LTE (2300/2500/2600 MHz)
3G: DC-HSPA+/HSPA+/HSPA/UMTS (900/2100 MHz)

Thats what i found for the frequencies of digicel antigua according to :

GSM bands	

    900 (E-GSM)

UMTS bands	

    B1 (2100)

UMTS protocols	

    HSPA+
    UTMS

LTE bands	

    B17 (700 bc)

LTE protocols	

    LTE

Other Operators according to my cellphone are:

Digicel-StaySafe
APUA inet
FLOW