Shells struck by the hundreds along the tense front lines in eastern Ukraine, drones monitoring a fragile cease-fire lost their way when the GPS signal they rely on was jammed, and then the cellphone network went dark.
In a sliver of land where pro-Russian separatists have battled for years against Ukrainian government forces, a group of international monitors tasked with keeping the peace reported more than 500 explosions in the the 24 hours ending Thursday midday, around four times as…
