I have the same amount of ETH incorrect shares dual mining with v11.4 as before over two rigs, at most 1 or 2 per 1000 shares. If you're getting more incorrect shares with v11.4, if probably means your settings were too high to begin with or a Bios mod with too aggressive timings. Use HwInfo to check for memory errors and adjust the memory clock down by 50 MHz until there are no more errors.
For most cases that will work, few cases if no memory errors then incorrect shares occur. Friend has many gpus with no memory errors and sometimes many incorrect shares. If any of you are getting incorrect shares, just lower memory clock speed until there are not any anymore.