Console error in setCache for slot element

[shunguoy]

Test page: https://www.ibm.com/us-en
Although the page scan looks fine, the console shows rule exceptions:

RULE EXCEPTION: text_spacing_valid /html[1]/body[1]/div[1]/div[1]/div[1]/dds-masthead-container[1]/dds-masthead[1]/#document-fragment[1]/div[1]/div[1]/div[1]/div[1]/slot[1]/dds-top-nav[1]/#document-fragment[1]/div[2]/div[1]/nav[1]/div[2]/slot[1]/dds-megamenu-top-nav-menu[1]/#document-fragment[1]/a[1] TypeError: Cannot read properties of null (reading 'nodeType')
at t.setCache (chrome-extension://lkcagbfjnkomcinoddgooolagloogehp/archives/preview/js/ace.js:2:512144)
at e.getAncestorWithStyles (chrome-extension://lkcagbfjnkomcinoddgooolagloogehp/archives/preview/js/ace.js:2:138488)
at Object.run (chrome-extension://lkcagbfjnkomcinoddgooolagloogehp/archives/preview/js/ace.js:2:488962)
at e.run (chrome-extension://lkcagbfjnkomcinoddgooolagloogehp/archives/preview/js/ace.js:2:172153)
at e.run (chrome-extension://lkcagbfjnkomcinoddgooolagloogehp/archives/preview/js/ace.js:2:174176)
at e.check (chrome-extension://lkcagbfjnkomcinoddgooolagloogehp/archives/preview/js/ace.js:2:202238)
at :1:346
at :1:1392

[philljenkins]

Slot (shadow DOMs) may not exist in the DOM/accessibility tree.
Also, is impacting performance.
But we need to find more examples of pages that use slots/shadow DOMs, or some other situation to be investigated such as nested slots.