I'm working on some tests with wdio 6 (on my way to upgrade it to 7) and I've been receiving this error on a very simple test

    it('Renders unit list', () => {
        $('.unit-list .bookable-unit-details:first-child').waitForDisplayed();
    });

While running the test I get this triggered a lot of times:

[0-0] 2021-07-14T20:20:56.077Z ERROR webdriver: Request failed with status 500 due to unknown command: POST /session/<HASH>/execute/sync
Build info: version: '3.141.59', revision: 'e82be7d358', time: '2018-11-14T08:25:53'
System info: host: '208-52-164-61', ip: '208.52.164.61', os.name: 'windows', os.arch: 'x86', os.version: '6.2', java.version: '1.8.0_181'
Driver info: driver.version: unknown

And at the very end:

[chrome 91.0.4472.106 windows #0-0] Error: waitUntil condition failed with the following reason: POST /session/<HASH>/execute/sync
Build info: version: '3.141.59', revision: 'e82be7d358', time: '2018-11-14T08:25:53'
System info: host: '208-52-164-61', ip: '208.52.164.61', os.name: 'windows', os.arch: 'x86', os.version: '6.2', java.version: '1.8.0_181'
Driver info: driver.version: unknown

Has anyone experienced this before? What was the solution?

EDIT

I've upgraded the wdio to the latest available and I'm still having this issue.

I've submitted an issue on wdio's github: https://github.com/webdriverio/webdriverio/issues/7145