Please first check that “Block all except contacts” is still enabled:
Callfilter.app → Filter priority
We have seen a few cases where this filter was disabled for an unknown reason.
For more stable work, I also recommend disabling all other filters in Filter priority and leaving only “Block all except contacts” enabled. This helps the app avoid unnecessary checks.
If the filter is enabled but unknown callers still come through, Android may be limiting Callfilter.app in the background. Please open: