I meet same issue before when I flashed PE10+, I looked for help by Google this problem, finally some one told me need to install this file first ( Disable_Dm-Verity_ForceEncrypt_03.04.2020.zip ) before flash the rom, then I solved the problem. Currently I had updated to the latest PE11+, and no more lag already.
U can try to download the zip file from below link, install the file from recovery mode, after that install the PE11+ ROM
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