bonienl

When no explicit gateway address is given for the subnet, then docker will assign the first address as gateway address. This is the conflict you see.
 
Under docker settings you need to set the specific subnet assignment for each VLAN, see example below
 

Remark: the upcoming Unraid version 6.10-rc5 has a new setting to enable or disable SMB multi-channel (it is disabled by default).
 

In 6.10 the read/write speeds are updated every 2 seconds.
 

If you don't want to capitalize device names, you can change the setting
 
Settings --> Display Settings --> Display device name = Raw
 

Getting a 169.254.xxx.xxx address means the system could not get an IP address from your router.
This suggests you have some network issue.
Try replacing cables and. moving ports on your switch or router.
You mentioned the message about interface eth0 down, this is another indicator that there is a network issue.
This interface should never go down, otherwise you loose connectivity.
 

The original check works fine for me, do you have SSL enabled for GUI access?
 
I tested your modification on my systems, there is no regression.
Made a change to use https instead of http for checking both plugins and docker.
Thx
 

The message about the share means the share is located on a disk (disk5), which is not part of the included disks / excluded disks list.
You need to update the included or excluded list if you want disk5 to be a member of the share.
Note: everything keeps working even with the mismatch in place (content is never touched)
 
This is the general setting to check
 Settings -> Global Share Settings -> Included/Excluded disks
 
This is the per share setting to check
 Shares -> <share name> -> Included/Excluded disks
 

Maximum size is the largest memory size your motherboard can support.
Usable size is what is actually available to the system.
 

I have been using Dune media players since 2009, and they work wonderfully.
The older models had only fast ethernet (100Mbps) connection. Dune uses their specific algorithm to read files from SMB, this is used when you enable “fast smb access”. Btw this setting does not exist anymore in nwer versions, which are optimised by default.
 
The graphic shows a constant reading (left) vs a lot of fluctuation (right), the latter part explains your stuttering.
 

Yes, disable bonding and enable bridging for eth0 (1G interface - br0) then add eth1 (2.5G interface) as member of the bridge.
Connect your PC to eth1 and it should get internet access thru the Unraid connection.