Thank you, Herve! I downgraded clover to r5119. Now everything seems to be okay except external display (it's native resolution is 2560x1440), that is connected to DisplayPort on PR02X docking station: it is blinking unevenly. I think of somehow tweaking frame buffer size. Am I heading in the right direction?
Also, I managed to use another config.plist (from E6230_Catalina_Clover_Pack_#2): I generated ssdt.aml and ssdt.dsl with ssdtPRGen.sh script, copied them to ACPI/patched as well as DSDT.aml and DSDT.dsl (from E6230_Catalina_Clover_Pack_#2 since I'm not sure how to generate them). With these files system is also stable, issue with external display still present.