Unreliable code completion in Kotlin

I'm having really annoying issue with code completion popups in Kotlin code. Whenever I start typing keyword/function/variable name, most of the time one of two things happen:

• popup with suggestions does not show up at all
• popup with suggestions shows up and then disappears very quickly

Whichever happens, trying to bring the popup again (Ctrl+Space) hardly ever helps, as most of the time the popup is being "auto-closed" again. See attached video demonstrating the issue (there's also one for code completion working fine in Java code). Note "Updating Indices"/"Indexing" showing up on the status bar for a split second... perhaps that's what "interrupts/discards" the popup?

Has anyone seen this before? Is it a known issue?

Upload id: 2020_11_05_RM3QchcBNM6tzdZf (files: code-completion-java.mov, code-completion-kotlin.mov)

IntelliJ IDEA 2020.2.3 (Ultimate Edition)
Build #IU-202.7660.26, built on October 6, 2020
Runtime version: 11.0.8+10-b944.34 x86_64
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macOS 10.15.7
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Non-Bundled Plugins: Karma, org.jetbrains.kotlin, com.intellij.plugins.html.instantEditing, Lombook Plugin, de.platon42.cajon, com.viartemev.requestmapper, mobi.hsz.idea.gitignore, com.alayouni.ansiHighlight, String Manipulation, detekt