Creator stops accepting key presses while editing for time periods of 1-2 seconds, then accepts them again for a few seconds. Rinse and repeat.

Cause seems to be regular crashes of the clang backend, as visible in the general messages:

2018-12-07T09:30:12 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:15 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:18 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:21 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:24 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:30 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:34 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:37 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:40 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:43 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:45 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:48 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:51 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:54 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:30:57 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.
2018-12-07T09:31:00 Clang Code Model: Error: The clangbackend process has finished unexpectedly and was restarted.

In the end, clang backend crashes for good. Minidump attached.