ASM block all whitelisted urls and parameters in standby device

Have you followed article https://support.f5.com/csp/article/K12200102

You also do a full sync to clear any issues:

https://support.f5.com/csp/article/K63470472

Also sometimes the incremental cache of 1024 for incremental sync needs to be increased to 2048 for example to stop such issues:

https://techdocs.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/big-ip-device-service-clustering-administration-14-0-0/05.html

I would also suggest to check the F5 bug tracker and release notes and to upload a qkview to ihealth for your error as your version may have some bug like an asm bigip process for example the asm_config_server needing a restart with bigstart  (https://support.f5.com/csp/article/K9073) etc.

bug Tracker:

https://support.f5.com/csp/bug-tracker?sf189923893=1

example release notes:

https://techdocs.f5.com/kb/en-us/products/big-ip_ltm/releasenotes/related/relnote-supplement-bigip-15-1-4.html

F5 ihealth:

https://www.f5.com/services/training/free-training-courses/getting-started-with-big-ip-ihealth

Just as a security note your policy being in trensperant mode on the active device is normal for the F5 device to not block the traffic but this means that you had a security risk till now so just to know that! Better clear the false positives and make the policy to be in blocking on the active and standby devices:

https://support.f5.com/csp/article/K70544352