I think you can’t have a list of values for a date or date/time type of key 
…
Your modified key should probably be set to list (as there are multiple values) instead of date (which accepts only one date)
Edit: Because this got me curious 
…
After some testing, if you actually set the modified key to date & time, you’ll see that the 2nd date in the list is interpreted as the beginning of the time part…
Having this in Source Mode:
---
modified:
- 2024-08-31
- 2024-09-01
---
Test
Results in this in Live Preview (from the Sandbox Vault):
So the 2nd date seems to be “merged” with the 1st date…
Which could partially explain why clicking on the Daily Note link icon fails: The value within the the YAML isn’t really read as a date but as a somewhat strange looking/a bit malformed date/time (At least, this is how I interpret it … and I could be completely wrong 
)
There could still be a bug in all this, imho: Properties should be able to see and inform you, through the “type mismatch” warning icon, that the type of key used (date) isn’t the right one, I think …
That is, if my assumption about the date and date & time types of key is correct: Only one date is allowed (expected to work properly) in a date type of key, only one date/time is allowed (expected to work properly) in a date & time type of key and any keys meant to store multiple values should be set to list .
Copying & pasting in a note without any YAML/Properties, in Source mode, the bits of markdown I shared here (above) and then switching to Live Preview, Properties automatically reads and parse the modified key as a List (which is what I expected) … But then setting that same key from Properties to date or date & time doesn’t seem to trigger the type mismatch warning either 
(like it does for any other types of key: text, number, etc…) …
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