Theme not loading in control panel for a custom channel after upgrade to EE 3.5.11

Dear Support, I just ran a local upgrade of EE from 2.8.1 to 3.5.11. The upgrade succeeded although I’ve noticed for one of my custom channels, when I go to enter or edit an entry in the Control Panel, the theme won’t load, causing the page to render without styling. Also, upon saving the entry, this exception is thrown:

Exception Caught SQLSTATE[42S02]: Base table or view not found: 1146 Table ‘surly_dev.exp_channel_grid_field_2’ doesn’t exist: SELECT * FROM (exp_channel_grid_field_2) WHERE entry_id = 16621 ee/legacy/database/drivers/mysqli/mysqli_connection.php:122 Stack Trace: hide details #0 ee/legacy/database/drivers/mysqli/mysqli_driver.php(137): CI_DB_mysqli_connection->query(‘SELECT *\nFROM (…’) #1 ee/legacy/database/DB_driver.php(297): CI_DB_mysqli_driver->_execute(‘SELECT *\nFROM (…’) #2 ee/legacy/database/DB_driver.php(203): CI_DB_driver->simple_query(‘SELECT *\nFROM (…’) #3 ee/legacy/database/DB_active_rec.php(1219): CI_DB_driver->query(‘SELECT *\nFROM (…’) #4 ee/legacy/models/grid_model.php(356): CI_DB_active_record->get(‘channel_grid_fi…’) #5 ee/EllisLab/Addons/grid/libraries/Grid_lib.php(246): Grid_model->get_entry(16621, 6, ‘channel’) #6 ee/EllisLab/Addons/grid/ft.grid.php(64): Grid_lib->validate(NULL) #7 [internal function]: Grid_ft->validate(NULL) #8 ee/legacy/libraries/api/Api_channel_fields.php(409): call_user_func_array(Array, Array) #9 ee/EllisLab/ExpressionEngine/Model/Content/FieldFacade.php(158): Api_channel_fields->apply(‘validate’, Array) #10 ee/EllisLab/ExpressionEngine/Model/Content/ContentModel.php(274): EllisLab\ExpressionEngine\Model\Content\FieldFacade->validate(NULL) #11 ee/EllisLab/ExpressionEngine/Service/Validation/Validator.php(262): EllisLab\ExpressionEngine\Model\Content\ContentModel->validateCustomField(‘field_id_6’, NULL, Array, Object(EllisLab\ExpressionEngine\Service\Validation\Rule\Callback)) #12 [internal function]: EllisLab\ExpressionEngine\Service\Validation\Validator->EllisLab\ExpressionEngine\Service\Validation{closure}(‘field_id_6’, NULL, Array, Object(EllisLab\ExpressionEngine\Service\Validation\Rule\Callback)) #13 ee/EllisLab/ExpressionEngine/Service/Validation/Rule/Callback.php(42): call_user_func(Object(Closure), ‘field_id_6’, NULL, Array, Object(EllisLab\ExpressionEngine\Service\Validation\Rule\Callback)) #14 ee/EllisLab/ExpressionEngine/Service/Validation/Validator.php(198): EllisLab\ExpressionEngine\Service\Validation\Rule\Callback->validate(‘field_id_6’, NULL) #15 ee/EllisLab/ExpressionEngine/Service/Validation/Validator.php(159): EllisLab\ExpressionEngine\Service\Validation\Validator->_validate(Object(EllisLab\ExpressionEngine\Model\Channel\ChannelEntry), true) #16 ee/EllisLab/ExpressionEngine/Service/Model/Model.php(484): EllisLab\ExpressionEngine\Service\Validation\Validator->validatePartial(Object(EllisLab\ExpressionEngine\Model\Channel\ChannelEntry)) #17 ee/EllisLab/ExpressionEngine/Model/Channel/ChannelEntry.php(174): EllisLab\ExpressionEngine\Service\Model\Model->validate() #18 ee/EllisLab/ExpressionEngine/Controller/Publish/AbstractPublish.php(272): EllisLab\ExpressionEngine\Model\Channel\ChannelEntry->validate() #19 ee/EllisLab/ExpressionEngine/Controller/Publish/Edit.php(475): EllisLab\ExpressionEngine\Controller\Publish\AbstractPublish->validateEntry(Object(EllisLab\ExpressionEngine\Model\Channel\ChannelEntry), Object(EllisLab\ExpressionEngine\Model\Content\Display\LayoutDisplay)) #20 [internal function]: EllisLab\ExpressionEngine\Controller\Publish\Edit->entry(‘16621’) #21 ee/EllisLab/ExpressionEngine/Core/Core.php(189): call_user_func_array(Array, Array) #22 ee/EllisLab/ExpressionEngine/Core/Core.php(94): EllisLab\ExpressionEngine\Core\Core->runController(Array) #23 ee/EllisLab/ExpressionEngine/Boot/boot.php(151): EllisLab\ExpressionEngine\Core\Core->run(Object(EllisLab\ExpressionEngine\Core\Request)) #24 admin.php(143): require_once(‘…’) #24 admin.php(143): require_once(‘…’)

The table, ‘exp_channel_grid_field_2’, mentioned above does not exist in the database (pre- or post upgrade). Also, I’ve checked the Settings, and the Themes folder is correctly pointed to.

Any recommendations on how to fix greatly appreciated.

Best, Louise