Your users care more about accomplishing their tasks than your brand (or your logo). Focus all your efforts on moving them forward towards improving their lives. They will come back if you are successful in doing that.
Oftentimes this kind of push can come from a marketing dept that is under pressure to build awareness. The best brand awareness will come from successful experiences.
Mobile design is hard enough, considering the space constraints, and busy distracted users. You want to get them through their tasks to accomplish their goals as quickly and effortlessly as possible.
1. Don't make me think
Consider the cognitive load you may place on your users, from the Neilsen Norman Group:
The total cognitive load, or amount of mental processing power needed to use your site, affects how easily users find content and complete tasks.
Every action where a user has to pause to understand its consequences is a tax on your customers' capacity, attention, and energy.
2. Ignore established patterns at your peril
Material design has established the floating action button as a convention as follows:
A floating action button (FAB) represents the primary action of a screen.
Users develop a model about what a control (or a logo!) is supposed to do:
Build on existing mental models: People already have mental models about how websites work, based on their past experiences visiting other sites. When you use labels and layouts that they've encountered on other websites, you reduce the amount of learning they need to do on your site.
3. Finally, ask yourself
Ask the question: 'Is viewing our company logo and pausing to figure out why it's taking up valuable real estate (or what it might do) helping our users accomplish the goals our application is meant to help them achieve?'