This is likely caused by issue #28318.

If you do go run golang.org/x/build/maintner/cmd/maintserve -http=localhost:8080, then visit http://localhost:8080/go.googlesource.com/go and search for "#142537", you'll see that maintner reports that CL as not having any tags:

As a result, gopherbot doesn't believe that the CL has a wait-author tag, so it doesn't try to remove it.

A simple program that confirms it:

package main

import (
	"context"
	"fmt"
	"log"

	"golang.org/x/build/maintner/godata"
)

func main() {
	corpus, err := godata.Get(context.Background())
	if err != nil {
		log.Fatalln(err)
	}
	cl := corpus.Gerrit().Project("go.googlesource.com", "go").CL(142537)
	fmt.Printf("tags = %q\n", cl.Meta.Hashtags())

	// Output:
	// tags = ""
}

Note here too. I volunteered for the fix of the corresponding issue #25253.

Tags are now correctly displayed on a local test run:

And the linked issue:

Change https://golang.org/cl/152779 mentions this issue: maintner: fix GerritMeta.Hashtags to look at earlier meta parents for answer

gopherbot was re-deployed with the maintner fix.