Hi Daniel,
review your configuration of search string. Use transactions below for configure and testing.
You may need to create a separated search strings.
If you use prefixed number like 50###?
T-code FEBSTS - search string simulation
T-code OTPM - set search string algorithm
Look documentation again that says about start and finishes of search:
Define Search String for Electronic Bank Statement - Bank Accounting - SAP Library
Hope could be helpful.
Regards,
Cristiano