Is this normal in the opening days of the connection? Or do I have to kick the Openreach device?
If you are getting errors in the VDSL2 data transfer, then DLM will intervene, and attempt to get rid of those errors - usually by adding a level of FEC and interleaving.
If the intervention isn't enough, then DLM will intervene further, setting higher levels of FEC and interleaving, until it finds a setting where the errors disappear, or at least minimise.
In the most extreme cases, it may also add "banding" where it restricts your sync speeds.
Most interventions cause a reduction in sync speed and an increase in latency.
Usually, your line is left to run free for the first two days, and DLM will only intervene on the third day. If it does, you will see a resync somewhere between 2AM and 8AM overnight. Further interventions are likely to be at similar times on subsequent days.
Kicking the Openreach modem almost never has an effect.
If the cause of errors gets removed, then it can take a number of weeks for DLM to reduce or remove the intervention. Kicking the modem won't speed this process up either.