There is an error in Timeline block when it tries to show a planned event if the course full name or the activity full name contain a backslash '\'.

Examples:
'Backslash \ chat name'
'Backslash \ course name'

When there is a backslash in the course name.
SyntaxError: Unexpected token   in JSON at position 53
    at JSON.parse (<anonymous>)
    at Renderer.stringHelper (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:362:6773)
    at Renderer.<anonymous> (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:362:8141)
    at Writer.renderSection (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:8035)
    at Writer.renderTokens (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:6836)
    at Writer.renderPartial (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:9198)
    at Writer.renderTokens (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:6995)
    at Writer.renderSection (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:7634)
    at Writer.renderTokens (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:6836)
    at Writer.renderPartial (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:9198)

When there is a backslash in the chat name.
SyntaxError: Unexpected token   in JSON at position 22
    at JSON.parse (<anonymous>)
    at Renderer.stringHelper (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:362:6773)
    at Renderer.<anonymous> (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:362:8141)
    at Writer.renderSection (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:8035)
    at Writer.renderTokens (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:6836)
    at Writer.renderPartial (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:9198)
    at Writer.renderTokens (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:6995)
    at Writer.renderSection (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:7634)
    at Writer.renderTokens (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:6836)
    at Writer.renderPartial (https://communitymoodle39.p72.demo3.opentechnology.ru/lib/requirejs.php/1647854186/core/first.js:529:9198)

Steps:

(course case)

1. Create a user.
2. Make sure there is a visible timeline block in the user dashboard.
3. Create a course with a backslash in its name (Backslash \ course name).
4. Enrol the user on the course.
5. Create a chat with no backslashes in its name in the course (Regular chat name).
6. In the chat instance settings in "Chat session" section set "Next chat time" to tomorrow or the day after tomorrow.
7. In the chat instance settings in "Chat session" section set "Repeat/publish session times" to "At the same time every week".
8. Login as the user and navigate to the dashboard.
9. Wait a little for AJAX requests to execute and the error to appear in modal.

(chat case)

1. Create a user.
2. Make sure there is a visible timeline block in the user dashboard.
3. Create a course with no backslashes in its name (Regular course name).
4. Enrol the user on the course.
5. Create a chat with a backslash in its name in the course (Backslash \ chat name).
6. In the chat instance settings in "Chat session" section set "Next chat time" to tomorrow or the day after tomorrow.
7. In the chat instance settings in "Chat session" section set "Repeat/publish session times" to "At the same time every week".
8. Login as the user and navigate to the dashboard.
9. Wait a little for AJAX requests to execute and the error to appear in modal.

Seems related to https://tracker.moodle.org/browse/MDL-67640