Regarding the changes implemented for the Inventory data import from Amazon, M2E Pro versions 6.4.3. and lower (for Magento v 1.x) might experience problems displaying 3rd Party Listing Titles starting from the end of June - begining of July, 2016. It is highly possible that the 3rd Party Listing Titles can be removed not only for the newly imported Items, but for the already existing 3rd Party Listings.
As a solution, you can upgrade your M2E Pro to at latest version 6.4.4 (for Magento v 1.x). The upgrade will allow the Amazon 3rd Party Listing Titles to be automatically recovered within 24 hours. However, those 3rd Party Listing which are imported after the upgrade will contain '--' in their titles. Import of the original Titles is impossible for such Items.
This issue does not affect Amazon Products which are placed and managed in M2E Pro Listings.
No functional limitation are applied to those 3rd Party Items which are missing their Titles. Generally, Title values of the 3rd Party Items are used in order to make the navigation more convenient and apply automatic 3rd Party Listings mapping by Title (it appears to be helpful in rather rare cases as Magento Product Name and Amazon Product Title are often totally different for the same Item).
We appreciate your understanding of the case.