Yes that is normal. If you have ever watched YouTube videos of RV manufacturers slathering on the adhesive and rolling out the membrane you would see why.
It is likely where the adhesive was thick and has no where to go.
It shouldn't be a problem.
Steve Rinker
Rochester, NY
2013 Keystone Sydney 340FBH 5th Wheel, 12,280 lbs loaded (scale)
2015.5 GMC Sierra Denali 3500, SRW, Duramax, CC, Payload 3,700 (sticker- not scaled yet)
Take my posts for what they are, opinions based on my own experiences.