Steps to reproduce:

1. Create a course and a chat activity in it
2. Do some chat messaging
3. Enable the TeX notation filter (configured to filter content and headings)
4. Add TeX notation to the name of the course:

$$a$$ MoodleMobile Developer Testing Course

1. Open the chat reports page

Full trace:

Warning: Attempt to read property "id" on null in /opt/app/lib/navigationlib.php on line 1551
Coding error detected, it must be fixed by a programmer: The theme has already been set up for this page ready for output. Therefore, you can no longer change the theme, or anything that might affect what the current theme is, for example, the course.
Debug info: Stack trace when the theme was set up: <ul style="text-align: left" data-rel="backtrace"><li>line 1972 of /lib/setuplib.php: call to moodle_page->initialise_theme_and_output()</li><li>line 104 of /filter/tex/filter.php: call to bootstrap_renderer->__call()</li><li>line 210 of /filter/tex/filter.php: call to filter_text_image()</li><li>line 176 of /lib/filterlib.php: call to filter_tex->filter()</li><li>line 232 of /lib/filterlib.php: call to filter_manager->apply_filter_chain()</li><li>line 1538 of /lib/weblib.php: call to filter_manager->filter_string()</li><li>line 1389 of /lib/pagelib.php: call to format_string()</li><li>line 56 of /mod/chat/report.php: call to moodle_page->set_heading()</li></ul>
Error code: codingerror
Stack trace:

line 2190 of /lib/pagelib.php: coding_exception thrown
line 1145 of /lib/pagelib.php: call to moodle_page->ensure_theme_not_set()
line 1228 of /lib/pagelib.php: call to moodle_page->set_course()
line 2860 of /lib/moodlelib.php: call to moodle_page->set_cm()
line 58 of /mod/chat/report.php: call to require_login()

Coding error detected, it must be fixed by a programmer: The course you passed to $PAGE->set_cm does not correspond to the $cm.
Debug info:
Error code: codingerror
Stack trace:

line 1226 of /lib/pagelib.php: coding_exception thrown
line 4807 of /lib/navigationlib.php: call to moodle_page->set_cm()
line 4343 of /lib/navigationlib.php: call to settings_navigation->load_module_settings()
line 833 of /lib/pagelib.php: call to settings_navigation->initialise()
line 962 of /lib/pagelib.php: call to moodle_page->magic_get_settingsnav()
line 226 of /lib/classes/navigation/views/secondary.php: call to moodle_page->__get()
line 890 of /lib/pagelib.php: call to core\navigation\views\secondary->initialise()
line 962 of /lib/pagelib.php: call to moodle_page->magic_get_secondarynav()
line 70 of /theme/boost/layout/drawers.php: call to moodle_page->__get()
line 1477 of /lib/outputrenderers.php: call to include()
line 1403 of /lib/outputrenderers.php: call to core_renderer->render_page_layout()
line 2979 of /lib/outputrenderers.php: call to core_renderer->header()
line 390 of /lib/setuplib.php: call to core_renderer->fatal_error()
line ? of unknownfile: call to default_exception_handler()