I concur with @hnyman, a total of 445Mbps is quite hard for a software shaper like cake, you will need quite capable hardware to allow that.
This could just show your router running out of CPU at ~34Mbps, but it also could mean that you instantiated the shaper on a LAN interface, in that case the "download" field in luci-app-sqm will actually control the upload (in reality download should be called ingress and upload egress; these names indicate the fact that the directionality is always in relation to the actual ethernet interface and not the internet. Thing about it packets leaving an interface are "egress", but for the WAN interface that corresponds to internet upload, while for a LAN interface (connected to internal hosts) the same leaving egress packets now correspond with internet downloads).
Could you please post the output of (log into your router via SSH* and issue the commands below without the double quotes):
"cat /etc/config/sqm"
"tc -s qdisc"
and a link to the detailed results of a dslreports speedtest (see https://forum.openwrt.org/t/sqm-qos-recommended-settings-for-the-dslreports-speedtest-bufferbloat-testing/2803 for recommendations how to configure that test). Ideally you would run that test once without sqm enabled (log into the router and issue "/etc/init.d/sqm stop") and once with sqm enabled ("/etc/init.d/sqm stop")
If at all piece_of_cake.qos should be slightly less expensive CPU-wise.
*) See https://www.turris.cz/doc/en/howto/ssh for instructions how to ssh into your router. I guess you already know that, but in the spirit of making this thread maximally useful to other's stumbling over it I wanted to add that here.