I believe that this is the fourth time that ISIS has attempted to relieve their besieged forces in Manbij, and it is not as big as some earlier efforts, where similar sized forces attacked simultaneously from the South and West as well.
Out in the countryside, ISIS suffers many more casualties relative to SDF than they do in the city - and faster. It is a big advantage to fight them in the open, where the Kurds have better long range snipers, can effectively use air strikes, and where booby traps and IEDs can't be used much, and where there are fewer human shields for ISIS. ISIS typically gets 100-200 killed per day during these kinds of operations (but maybe half that this time), vs. a few dozen per day in the city. (they are still being killed in the city as well during this). ISIS has also unsuccessfully tried to break out from the city a few times. They may try again, if the relief force gets close enough. There is an offer to let them go if they release the hostages. Some estimates are that ISIS is down to the last 100, or less, inside the city - so it does not have much longer to make a run. Civilians are returning to parts of the city away from the last holdouts.
In Aleppo, 3,000 islamist rebels (formerly called Jahbat al Nusra, who recently renounced allegiance to al Queda and renamed themselves Jabhat Fateh al-Sham) have broken through the siege of Eastern Aleppo (which you reported the regime had recently achieved), reopening rebel supply lines there. The fighting is heavier there, but the airstrikes are Russian (much less accurate) and most of the ground forces are better equipped but less effective Syrian Army, Lebanese Hizbullah, and other Iranian militias raised in Iraq and Afghanistan. A large group of Kurds has long been surrounded in Northern Aleppo. They hold the ethnically Kurdish Sheik Masood neighborhood - they are the local residents. The Syrian regime is building up for another attack, to cut the supply lines and re-impose the siege on islamist rebels in Eastern Aleppo.
