I see the loss of custom bitrate post reboot on the following models with firmware versions. All are upgradable, English versions from Andy except the last one.
Dahua IPC-HDW5541H-AS-PV 2.800.0000000.6.R, Build Date: 2019-08-01
Dahua
SD1A404XB-GNR 2.800.0000000.15.R.P9.4a8, Build Date: 2019-08-02
Dahua PTZ SD49225T-HN 2.800.0000000.4.R.R4.2510.9A.NR, Build Date: 2019-11-05
Dahua IPC-HFW5231E-Z12E 2.800.0000013.0.R, Build Date: 2019-12-02
Dahua SD1A203T-GN 2.800.0000000.4.R.R4.383, Build Date: 2019-11-05
Dahua IPC-HDW4631C-A 2.460.GP01.16.R, Build Date: 2017-09-04
I thought of using a python script to periodically set the bit rate, but the API command doesn't seem to work for the newest firmware. Only returns error.
The following works only on old 2017 firmware
http://<ip>/cgi-bin/configManager.cgi?action=setConfig&Encode[0]MainFormat[0].Video.BitRate=8960
Have not found a newer API with a different command yet.