Hi @Sjoerd and welcome to the KNIME forum !
Please find here below a possible solution:
and the workflow:
20210721 Pikairos Generate counter sequence upon certain value.knwf (36.2 KB)
An easier solution is possible with just a Java snippet node based on Java programming.
Hints on how to solve it using Java can be found in the recent post Java snippets have long memories!... by @Takbb.
Hope this helps
Best
Ael