http_process_state_prepend - Invalid action:0x109041

Version 12.1.2 HF1

After upgrading from version 11 one of our customer's sites was failing with this error

Nov 13 09:14:56 lb1 err tmm3[22668]: 011f0016:3: http_process_state_prepend - Invalid action:0x109010 Server sends too much data. serverside (XXX.XXX.XXX.XXX%102:80 -> XXX.XXX.XXX.XXX%102:57527) clientside (XXX.XXX.XXX.XXX%102:64740 -> XXX.XXX.XXX.XXX%102:443) (Server side: vip=/external/vip_443 profile=http pool=/external/pool server_ip=XXX.XXX.XXX.XXX)

I found info here https://devcentral.f5.com/questions/http-process-state-prepend-server-sends-too-much-data-49488 One of the solutions was a short, sweet iRule, which I preferred as it didn't makes changes to the whole unit. (the other one was tmsh modify sys db tmm.http.passthru.invalid_content_length value enable)

the iRule is this

when HTTP_RESPONSE { 
if { [HTTP::header exists "Content-Disposition"] } { 
HTTP::disable } }

Now the customer says their site is fine, and I don't get that error anymore BUT I constantly get this error in LTM on their site:

Nov 14 13:19:12 lb1 err tmm[22668]: 011f0007:3: http_process_state_prepend - Invalid action:0x109041 clientside (XXX.XXX.XXX.XXX%102:49303 -> XXX.XXX.XXX.XXX%102:443) serverside (XXX.XXX.XX.XXX%102:80 -> XXX.XXX.XXX.XXX%102:53992) (Client side: vip=/external/vip profile=http pool=/external/pool client_ip=XXX.XXX.XXX.XXX)

Any idea why? Thank you very much

Misty