Siran,
An afterthought... give this approach a try since you are trying to display a linked table data in collector.
1) Remove the joins in your map on the ArcGIS platform you are publishing from
2) Add a Relationship Class to the database between the feature class and table you need to link the data. Note that a relationship class is not the same as creating a in memory join or relates. If needed, please see Creating a Simple Relationship Class for additional information. You will need a relationship class for each feature class to be linked to the table. Although, all of the feature classes can point to the same table, if needed.
3) Publish the feature classes and table to AGOL as feature Service. The relationship classes will transfer when you publish the data.
4) Create a AGOL Map with the data published and save. Please insure at least one feature is editable so it will show in the available maps to Collector.
5) Open the Map in Collector.
6) Select a feature that has a relationship class to the underlying table. A link will be available to the table row in the attribute information for the feature selected as shown below.
7) Select that link and the information from the linked row will be displayed. You can even edit the data by selecting Edit, if enabled.
I hope this is helpful. let me know if you have any questions.