There is a temporary special gift in the Gift Screen named Mega Reinforcements Pack.

I sent it to some friends, so they could send it back to me again later.

Upon accepting the gifts in my inbox, the reinforcements from this pack weren't added immediately.

I needed to refresh my page afterwards to have them added.

It seems each pack contains 4 reinforcements.

yep, old, same for mega coins & ultra coins

Will look into this, thanks for the report!