The updated version of mvm_machine_attacks_ep6 has been rejected because the map was updated but its name is unchanged.
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The issue with mvm_overlord_b3 not showing on server 6's map votemenu was not properly fixed. It is now fixed.

I fell asleep before I could finish adding the maps mvm_machine_attacks_ep6 and mvm_overlord_b3. Both maps are now added.

In addition, mvm_underground_b1 and mvm_overlord_b2 (now b3) were missing on server 6's map votemenu. This is now fixed.

The updated version of Machine Attacks ep3 has been rejected because the map was not renamed to reflect that it has been updated. This means that if I were to add the updated version of EP3 to the Machine Attacks server, it will reject players who already have the old version of EP3 installed.

I'll see if I can get redmyclan (The creator of the Machine Attacks maps) to fix the map transition issues with the Machine Attacks maps so that upon completion of each map, the map just switches to the next map as defined in the MvM missioncycle instead of having the name of the next map hardcoded to the map itself, if this is possible to accomplish with the maps.

mvm_hydro_a2 has been added to all servers.
If it isn't listed on the votemenu yet, a map change has to be done first.

The 'wave 0' issue in mvm_killing_fortress2, which was caused by me rushing the addition of that map and thus forgetting to add the popfile, has been fixed.

Up next is mvm_overlord.

ep4 is already added. ep3 was removed because of a bug in ep2's mapchange to ep3.
Up next is mvm_hydro_a2 and then mvm_overlord (Which I have yet to spawn test)

mvm_hydro_a1 has been rejected because it causes server crashes.
Next up is mvm_machine_attacks_ep4 and then mvm_overlord.

I'll look into mvm_hydro_a1 and mvm_overlord tomorrow.

update above.

I am one of those experiencing this, so here is my output of nslookup
I'm getting a download speed of 14KB/s

This thread is for anyone experiencing slow download speeds when downloading a map in-game. If you are experiencing slow download speeds provided this is not caused by your Internet connection, include the following information in your post:
- The output of the following command
in the Command Prompt (Windows) or terminal (Linux)
- What download speed you get when downloading a map from tf2servermaps.cdnserv.sandydprod.net Try downloading this map[tf2servermaps.cdnserv.sandydprod.net].

I have notified SandyD of this problem. An update will be posted when this is fixed.