Conflicts and Power Clashes between Functional Managers and Project Managers

Much of this should be resolved with a strong project charter and risk management plan. The charter should define roles and responsibilities and the interaction between the stakeholders both within and external to the project. Hopefully by addressing these issues at the start of the project it can avoid conflict later on. I keep harping on risk-driven project management and conflict between the functional and project requirements are high on the risk register, not only at the leadership level but with project assigned personnel as well. Being accountable to two bosses is never comfortable - is demotivating and counter-productive.
Identify the risk, provide mitigating measures, address these in the project charter before it becomes a problem. When it becomes a problem implement the pre-determined measures and hopefully keep the boat on an even keel.

A very strong and clear thoughts from the seniors here, I’m following in the background, thanks for bringing up this topic Joao!

It's all about the Ego . The Bigger and Bloated the Ego is of the Functional Manager or the Project Manager, the bigger the clash between the two .

Assuming you are the PM at the receiving end of the difficult Functional Manager:-
Strategy 1 :- Be Polite , be persuasive, try all the good stuff that our colleagues have stated like perspective taking , empathy .
Strategy 2:- Assume that there are hidden agendas or political bun-fights beyond your control that maybe at play and try to steer your project the best you can by being civil and respectful .

Sometimes it may be in their nature to be difficult and captious. You really cannot help it or change them. So you invent new ways to handle them.

Sometimes you keep escalating to your sponsor to resolve the issue till the cows come home , but nothing may happen because that Functional Manager may be reporting to someone that may wield a stronger political whip than your sponsor.

If on the other hand you have the bloated ego and are narcissistic enough to not notice it , it will be a matter of time before the Guillotine hits your neck !

It's all about the Ego . The Bigger and Bloated the Ego is of the Functional Manager or the Project Manager, the bigger the clash between the two .

Assuming you are the PM at the receiving end of the difficult Functional Manager:-
Strategy 1 :- Be Polite , be persuasive, try all the good stuff that our colleagues have stated like perspective taking , empathy .
Strategy 2:- Assume that there are hidden agendas or political bun-fights beyond your control that maybe at play and try to steer your project the best you can by being civil and respectful .

Sometimes it may be in their nature to be difficult and captious. You really cannot help it or change them. So you invent new ways to handle them.

Sometimes you keep escalating to your sponsor to resolve the issue till the cows come home , but nothing may happen because that Functional Manager may be reporting to someone that may wield a stronger political whip than your sponsor.

If on the other hand you have the bloated ego and are narcissistic enough to not notice it , it will be a matter of time before the Guillotine hits your neck !

Thank you dear Joao for raising such topic. It deeply touches the issues I faced in my previous organisation (Weak Matrix).

During my 1st few weeks of execution, I had so many difficulties to get the job done without aligning all the stakeholders (weak experience).
But after I figured out what the root causes are for my issues I started acting by:
- Getting the alignment of all stakeholders on the planned work.
- Implementing a governance model to track and escalate.
- Conducting an awareness session for the resources who are not from my department about the project and what is their exact rule in executing.

After less than a month from these arrangements, things went smoothly and progress got back in track.