Expected Behavior:

On updating an option page to get a single 'Settings Updated' message, even when multiple plugins use CMB2 Options pages.

Actual Behavior:

Depending on how many plugins are loaded with CMB2 option pages you can get multiple 'Settings Updated' message

Steps to reproduce (I have confirmed I can reproduce this issue on the trunk branch):

1. create a 2 plugins with different option pages
2. activate just one / activate two
3. trace code with debugger

CMB2 Field Registration Code:

Not applicable

Proposed fix:

cmb2/includes/CMB2_Options_hookup.php
line 109 onwards

if ( ! empty( $_GET['settings-updated'] ) ) {
			if ( 'true' === $_GET['settings-updated'] ) {
				add_settings_error( "{$this->option_key}-notices", '', __( 'Settings updated.', 'cmb2' ), 'updated' );
			} else {
				add_settings_error( "{$this->option_key}-notices", '', __( 'Nothing to update.', 'cmb2' ), 'notice-warning' );
			}
		}

checks settings-updates for every option page, so if multiple options pages this is true multiple times.
Adding a check against the page stops this e.g.

if ( ( ! empty( $_GET['settings-updated'] ) ) && ($this->option_key == $_GET['page'] ) ){
			if ( 'true' === $_GET['settings-updated'] ) {
				add_settings_error( "{$this->option_key}-notices", '', __( 'Settings updated.', 'cmb2' ), 'updated' );
			} else {
				add_settings_error( "{$this->option_key}-notices", '', __( 'Nothing to update.', 'cmb2' ), 'notice-warning' );
			}
		}

Pull request

I haven't yet, but happy to create a pull request if this makes sense