As this is still an issue with current Delphi versions: every now and then it looses which designers are needed for a frame:

[WayBack] What is the easiest way of getting Delphi to accept a newly added file as a frame and to treat it as such? – Stack Overflow (by Brian Frost)

<DCCReference Include="x\y\z\myFrame.pas">
  <Form>frameMy</Form> 
  <FormType>dfm</FormType>
  <DesignClass>TFrame</DesignClass>
</DCCReference>

Then check your .dfm file to see if it starts with the correct inherited or object as per Delphi – TInterfacedDataModule revisted – use ‘inherited’ in your .dfm files when your datamodules look like forms in the designer.

Oh and at design time, be very careful embedding frames. Better not to do it at all and for certain: do not embed frames in a nested way: [WayBack] Frames in 10.2.2 Hi Has anyone else had issues with frames under 10.2.2? The project seems to have lost its links to the frames? If I went to the Too… – Vince Bartlett – Google+

–jeroen

Reminder so self: [WayBack] sglienke / Spring4D / source / Source / Reactive / Spring.Reactive.pas — Bitbucket fragments:

type
  TInterlocked = SyncObjs.TInterlocked;
  TInterlockedHelper = class helper for TInterlocked // TODO: move to Spring.pas
    class function CompareExchange<T: IInterface>(var Target: T; const Value, Comparand: T): T; overload; static;
    class function Exchange<T: IInterface>(var Target: T; const Value: T): T; overload; static;
  end;

{$REGION 'TInterlockedHelper'}

class function TInterlockedHelper.CompareExchange<T>(var Target: T;
  const Value, Comparand: T): T;
begin
  Result := Default(T);
  PPointer(@Result)^ := CompareExchange(PPointer(@Target)^, PPointer(@Value)^, PPointer(@Comparand)^);
  if PPointer(@Result)^ = PPointer(@Comparand)^ then
  begin
    if Assigned(Value) then
      Value._AddRef;
  end
  else
    if Assigned(Result) then
      Result._AddRef;
end;

class function TInterlockedHelper.Exchange<T>(var Target: T;
  const Value: T): T;
begin
  Result := Default(T);
  PPointer(@Result)^ := Exchange(PPointer(@Target)^, PPointer(@Value)^);
  if Assigned(Value) then
    Value._AddRef;
end;

{$ENDREGION}a

–jeroen