Magento 2.2.2 Multi Select Attribute doesn't save when related products are attached

[magefan]

Preconditions

1. Magento 2.2.2
2. PHP 7.0.23
3. Browser Chrome 64 on Linux

Steps to reproduce

1. Add Multi Select Attribute to Product
2. Choose some options to that multi-select and save the product
3. Add related products and save
4. Try to change options in multi-select and save

Expected result

1. The options should have changed

Actual result

1. After the save and page refresh the options stay the same

The same issue had @AgentGod #4822 (comment) and the @duckchip #4822 (comment) solution helps but this just a temporary solution.

[magento-engcom-team]

@magefan, thank you for your report.
We've acknowledged the issue and added to our backlog.

[jajaramos]

#MLAU18

can't reproduce on Magento 2.2.2

[ctadlock]

I have this exact issue on Magento 2.2.3. I have a product with several multi-select attributes, everything works well. If I add an up-sell product, I am then unable to modify any of the multi-select attributes.

[ctadlock]

@jajaramos Please re-open this issue; @cherednichenkoa is working on a fix (#14125)

[A-1A]

I Found Solution after R&D On Magento database.
Login In your phpmyadmin
Go to your website database
Open "eav_attribute" table
Find Your multiselect "attribute_id"
Edit Row
If "backend_model" Column blank then paste this Magento\Eav\Model\Entity\Attribute\Backend\ArrayBackend
And Also Please check this
https://magento.stackexchange.com/questions/224621/warning-array-filter-expects-parameter-1-to-be-array/230444#230444

[DanBeckett]

Recently (Magento 2.3.3) experienced the same issue with a Multi-select attribute created via the Attribute editor in the dashboard. In eav_attribute found that the source_model was NULL, updating this to Magento\Eav\Model\Entity\Attribute\Source\Table fixed the issue for me.