I think there is a bug in HAL_TIM_DMABurst_WriteStart (in V1.15 at least), where the timer burst length is used both for the number of registers to write into the timer peripheral and the number of total DMA transfers. Thanks, Aris

[AEfth]

There is an identical discussion but for a different mcu:

https://community.st.com/s/question/0D50X00009XkdocSAB/timer-dma-burst-mode-arbitrary-waveform