Repair wrong chashes in tx_realurl_urldata table

ext_localconf.php

<?php

// Add Command controllers
if (TYPO3_MODE === 'BE') {
	$GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['extbase']['commandControllers'][] = \Lemming\Extension\Command\CacheHashCommandController::class;
}

Lemming\Extension\Command\CacheHashCommandController.php

<?php
namespace Lemming\Extension\Command;

use TYPO3\CMS\Core\Database\DatabaseConnection;
use TYPO3\CMS\Core\Utility\GeneralUtility;
use TYPO3\CMS\Frontend\Page\CacheHashCalculator;

class CacheHashCommandController extends \TYPO3\CMS\Extbase\Mvc\Controller\CommandController
{
    const TABLE = 'tx_realurl_urldata';

    /**
     * Repair CHashes
     *
     */
    public function repairCacheHashesCommand()
    {
        /** @var DatabaseConnection $databaseConnection */
        $databaseConnection = $GLOBALS['TYPO3_DB'];

        $entries = $databaseConnection->exec_SELECTgetRows(
            '*',
            self::TABLE,
            'request_variables LIKE "%cHash%"'
        );

        if ($entries == null) {
            $this->outputLine('No entries found');
            exit;
        }

        $this->outputLine(sprintf('Found %s entries with a cHash', count($entries)));

        /** @var CacheHashCalculator $calculator */
        $calculator = GeneralUtility::makeInstance(\TYPO3\CMS\Frontend\Page\CacheHashCalculator::class);

        $repaired = 0;
        foreach ($entries as $entry) {
            $this->outputLine(sprintf('Updating entry %d', $i));
            $requestVariables = json_decode($entry['request_variables'], true);

            $requestVariablesAsString = http_build_query($requestVariables);
            $cHash = $requestVariables['cHash'];
            try {
                $newCHash = $calculator->generateForParameters($requestVariablesAsString);

            } catch (\Exception $exception) {
                $this->outputLine('Error while generating new cHash for entry:');
                var_dump($entry);
            }

            if (isset($newCHash) && $newCHash != $cHash) {
                $newRequestVariables = $requestVariables;
                $newRequestVariables['cHash'] = $newCHash;

                $newRequestVariablesField = json_encode($newRequestVariables);
                $newOriginalUrlField = str_replace('cHash=' . $cHash, 'cHash=' . $newCHash, $entry['original_url']);
                $newOriginalUrlHashField = crc32($newOriginalUrlField);

                $databaseConnection->exec_UPDATEquery(
                    self::TABLE,
                    'uid=' . $entry['uid'],
                    [
                        'original_url' => $newOriginalUrlField,
                        'original_url_hash' => $newOriginalUrlHashField,
                        'request_variables' => $newRequestVariablesField,
                    ]
                );

                $repaired++;
            }
        }

        $this->outputLine(sprintf('Repaired %s entries', $repaired));
    }
}

Possibly needed while updating from 7.6 to 8.7

Needed only if your 7.6 did not include id to cHash but your 8.7 does ($GLOBALS['TYPO3_CONF_VARS']['FE']['cHashIncludePageId'] in one installation is different from the other). Otherwise it is not needed.