I've been struggling with Web Part connections on a classic page on our SPO tenant and would appreciate any feedback.
Scenario: An InfoPath list form has been created, which handles data and sets some field values to be made available to other Web Parts on the same page with the 'Send Data to Web Part' rule action. A second web part (Library View) consumes these using 'Get Parameters From' to use as part of some filter conditions.
It was necessary to create these parameters manually in SPD2013 code view due to the longstanding interface bug in that software which prevents the 'List View Tools' tab from appearing.
When I establish a web part connection between two List/Library View web parts, the 'Configure Connection -- Web page Dialogue' (.../_layouts/15/AspXform.aspx?pageUrl=...) appears correctly as long as no InfoPath Form Viewer web parts are present in the same page.
If any InfoPath Form Viewer web parts are present in the same page, even if they're not the source or destination of the intended connection, this dialogue does not appear.
For web part pages which only use 'Send Form To' an InfoPath Form Viewer web part from a connected view of its same list, this is managable - as the relevant binding is automatically established without any dialogue. As long as the Form is the last web part to be added, it can be made to work.
For other requirements, however, it is necessary to bind fields from the Form against the Parameters in some way. I still have access to a 2010 on-prem environment for a few weeks, and will try to replicate/generalise the '<WebPartPages:SPProxyWebPartManager runat="server" id="spproxywebpartmanager"><SPWebPartConnections>' syntax in SPO. This is not ideal and I expect to encounter further problems if this needs to be done at scale.
Is this a known bug/limitation with Classic Pages? I've tried various browsers - IE8-11, 32/64 bit, Edge/FF/Chrome, Compatibility Mode on/off, etc.
In principle we'd be willing to use Modern for this, but I've not found any Modern Page friendly way to inject the necessary pivoting we resolve with embedded InfoPath. If it needs to be said, yes, we are also aware that InfoPath is going EOL in a few years. PowerApps is not a viable solution in our environment at this time.